converting a GSM phone to another network.

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doug-doug the mighty's picture
Joined: Apr 14 2004
Posts: 1355

I am the proud new owner of a Cell phone module that plugs into my Handspring Visor PDA, giving me all the benefits of a cell phone and PDA without needed to cough up the cash for a new PDA. The phone uses the GSM 900/1900 standard and has a neat little place for me to switch the SIM card from my existing phone.

I recently learned that my current carrier NEXTEL uses something called IDEN and does not work with GSM (explaining the failure to plug-and-play). I had already planned to go to Verizon, but they use something called CDMA. And further investigation reveals at least two other formats used by other major carriers. Does anyone know how to go about converting a phone (in this case, my GSM-based PDA plug-in) to another network format? I am not scared of difficult projects, and the word 'impossible' only provokes me to prove you wrong.

I realize that this may be impractical, but the plug-in was a free gift and a new PDA phone is $400 (US) WITH a two year contract ($650 without) AND will be specific to whatever network my carrier of choice uses, meaning when I decided to drop them in 6 months for another money-grubbing whore of a carrier, my phone most likely will not work and I will be in the same predicament - pay through the nose for new hardware, or carry a separate phone and PDA.

I realize that this may require taking the 'free phone' I would get with new service and canabalizing it for the parts.

-- Doug-Doug The Mighty

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--DDTM ('Fritter Critter' since Apr 26 2004 - 18:16)

'If it ain't broke, take it apart anyways. If you can't take it apart, break it so that you can fix it.'

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Dr. Webster's picture
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Joined: Dec 19 2003
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A couple points: Sprint PC

A couple points:

Sprint PCS uses TDMA, as does Verizon *in some areas.* Verizon also uses GSM in other areas.

T-Mobile, AT&T, and Congular use GSM.

GSM phones are "locked" by their respective service providers. Some providers will give you the code to unlock your phone, thus letting you use it on another network.

There is no way to switch a GSM phone to TDMA or vice versa. It's a hardware difference. When I switched from Sprint to T-Mobile, I had to get a new phone.

So the short of it: provided you can unlock the phone module (or if it's already unlocked) then you're set to work on any GSM network. If you wanna go with iDEN, or TDMA, no dice.

You're not going to be able to cannibalize a new phone to hack the phone module to work. You'd basically have to completely redesign the module, and if you were capable of that, then you wouldn't have asked your question in the first place. Wink

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doug-doug the mighty's picture
Joined: Apr 14 2004
Posts: 1355
Good info...

Thanks.

My assumption is that the module is unlocked and usable for other GSM networks, but I would like to know for sure. The SIM card currently in place has no phone number associated with it and gives me access to all of the phone features (except the obvious one of being able to make a phone call). How can I find out for sure?

I trust you that the hardware is different, but just how much so is what I need to find out. Since, my module was free and my current contract costs too much to break at this moment, I see a future trip to the workbench to take apart yet another perfectly good, working piece of technology. I do still plan to learn what makes these phones different (hardware-wise), and what makes them similar (probally going to track down pinout information for some of the ICs).

This 'learning project' will take some time. I am just about to start a project to convert my Rev A iMac's CRT to a LCD display (just looking for that one last piece to make it all work), so I will post back with more questions in a week or four once I have had time to dig deeper.

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--DDTM ('Fritter Critter' since Apr 26 2004 - 18:16)

'If it ain't broke, take it apart anyways. If you can't take it apart, break it so that you can fix it.'

JetStar's picture
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Basicly what you are trying t

Basicly what you are trying to do would require an enginering degree, and Dr. Bob-like soldering skills and equipment.

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It must be user error.

doug-doug the mighty's picture
Joined: Apr 14 2004
Posts: 1355
Close

Well, I do have a degree in Physics and am pretty deft with an iron, with a strong eye for detail, but I conceed that my experience is not from professional training.

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--DDTM ('Fritter Critter' since Apr 26 2004 - 18:16)

'If it ain't broke, take it apart anyways. If you can't take it apart, break it so that you can fix it.'

Dog
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Joined: Dec 20 2003
Posts: 46
Now for doggy wisdom! There'

Now for doggy wisdom!
There's 2 versions of the Visorphone, a GSM sim card version and the sprint pcs version. I don't know what network sprint uses, that might be a better chance for reprogramming. As for working on a GSM phone to make it work on cdma n other networks you're looking at a new circuit board and chips and wiring and programming and other fun stuff. (all assumption based logic)

Unlocking should be easy now with the number transfering system in place. They (cellular providers) can't really tell you to piss off when you tell them you're moving to another network and need to unlock the phone.

Dog
My person sick reason for writing, make me an offer I want a visorphone for GSM ;D

doug-doug the mighty's picture
Joined: Apr 14 2004
Posts: 1355
Caveat

Thought about this after I wrote it and wanted to qualify my remark(s) prior to any backlash.

From a pure dumb skills point on things, I can definetely hold my own. I hold the likes of Dr. Bob in very high esteem and would not dare compare my working knowledge to their understanding or experiences. My approach is to systematically reverse engineer the object and gather technical info (pinouts, mfr data) and attempt to exploit other fetures or possibilties. This is how I wound up getting most of the pinouts for my mezz connector on my iMac and taking on an active project to convert my iMac's CRT to an LCD. It is also how I have produced schematics for a valve (aka vacuum tube) audio amplifier (just having trouble securing the needed parts at cheap prices). I am good at taking things apart and learning how they work, but things like HTML will always be a mystery to me.

My true area of expertise is in mainframe operating systems, knowledge management (aka metadata), photography, and where Einstien's theory of relativity fails (mass remains constant under a coordinate transformation). But I digress...

My whole take on things is that a project should challenge me and if it can work in theory, then it is worth the attempt. Solicitation from the experts along the way (the Dr. Bobs of the world) is expected. Failure of the whole project is acceptable only if I have tried my best (and my son has not accidentally thrown out all of my project notes as happened with my bass guitar project - three years of work and a very modular design albeit solid-state, he was only three then. Yes, I took it as a hint, although the act was innocent.)

So for the tangent, just did not want my last post to come across as an arogant slight against any of the fine folks in this community.

--DDTM

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--DDTM ('Fritter Critter' since Apr 26 2004 - 18:16)

'If it ain't broke, take it apart anyways. If you can't take it apart, break it so that you can fix it.'

doug-doug the mighty's picture
Joined: Apr 14 2004
Posts: 1355
Hmmm...

I will try to find out what the Sprint version used. My version was used with T-Mobile (according to the previous owner). When I had cracked this one open, I noted that all of the ICs of interest were enclosed in a EM shield that has soldered to the card, encasing everything. I was waiting to pull it off until I had a better take of the scope of this project.

Since Nextel wants $200 (per phone) to term the contract, I will keep them until things run out in October. My wife does not like the service area of any carriers with GSM have (by coincidence), so I do not know if we will every swith to a carrier that offers this. I will try to secure the rest of the accessories and will take your request under consideration. I would be looking for cost of shipment only since all of this is coming to me free anyways.

In the meantime, if I can come up with enough good technical data to plan my project, I will undertake the vivesection mentioned. I have some older cell phone lying around (many donated from friends and family) and just need to determine what network they were designed for as these are potential parts donors. The way things look right now, evrything from the connections to the speaker and antenna all the way to the 68pin microchannel connector will need to be reworked. This means a new PCB, not to mention the real possibility that some ICs have embedded logic/programming on them. (Hence my desire to rework vice copy from scratch).

--DDTM

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--DDTM ('Fritter Critter' since Apr 26 2004 - 18:16)

'If it ain't broke, take it apart anyways. If you can't take it apart, break it so that you can fix it.'

performaman's picture
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Sprint Network

I've got a Hitachi phone that I use with a Sprint account, and it uses CDMA. I got it 6 months ago.

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Egg freckles?

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Joined: Jul 27 2004
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I have a Sprint Visorphone th

I have a Sprint Visorphone that I'd be willing to send you if you'll pay shipping. I bought it for $10 new and only wanted the charger. I'm no longer using my Prism or the many accessories that I purchased and would be happy to contribute to your experimentation. Email me - zieak at yahoo.

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The phones for CDMA, TDMA, an

The phones for CDMA, TDMA, and GSM, while similar in appearance on the outside, are *VERY* different on the inside. You can't jump from one network type to another.

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Dr. Bob
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doug-doug the mighty's picture
Joined: Apr 14 2004
Posts: 1355
Since I first posted this thr

Since I first posted this thread, I have cracked open my phone module. I took a cursory inventory of the hardware and the layout. I got enough to see that this is definetely a challenge. Over the past few weeks, I have been playing out the possibilities in my head and I came to the conclusion that this hack will take a lot more time than I can give it. I really want to do this, but need to put it off for a few months due to some other more pressing personal demands on my time.

I do plan to start researching info on the chips and mapping out my approach, but do not expect to hear anything until I actually get somewhere. I have a dead iMac and a q950 that are just begging to be messed with and connected together. I also have a nursey to prepare and I may need to change jobs before all of this is done. I figure my chances of success on this are 1 in 60 at best. I will revive this thread in December - this is just the type of challenge I like, I just need to finish some other side projects.

--DDTM

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--DDTM ('Fritter Critter' since Apr 26 2004 - 18:16)

'If it ain't broke, take it apart anyways. If you can't take it apart, break it so that you can fix it.'