Bitcoin Forum

I have this idea: how could we start a bitcoin-over-GSM phonecall service? It should be possible to send bitcoins over a phonecall as a modulated audio stream. The only problem would be the storage, which has to be as a recording or binary data (transforme by some software in the smartphone)

GSM is a completely digital system. It should be possible to send this data over something like SMS, instead of using multiple D/A/D conversions that include lossy compression.

I agree that having simple apps for sending and receiving bitcoins for Iphone, Android and other mobiles would be uber-cool.  Mobile apps is where it's at.

Why would we use SMS or something else GSM-specific? Almost all smartphones capable of running third-party software have some sort of internet access.

I have a license to the SDK of the VeriFone Vx-series credit card payment devices... was thinking about how a Bitcoin app might work.  It would probably have to interface with something like MyBitcoin.com that can provide an instant commitment - they don't quite have the CPU or memory to participate as a full node, and waiting for a block would be infeasible for transaction speed.  They are programmed in C and they run a proprietary OS that mimics POSIX compliance in many respects.

I thought of this because a couple particular models, the Vx510G and Vx610, have a GSM radio built in.  Essentially they're a Siemens MC56 GSM radio module connected to a COM port embedded inside the terminal.  But such an application wouldn't be strictly limited to GSM, most of the other models have dialup modems and some sort of IP connectivity such as Ethernet.

For a phone without internet access, just use touch-tone from the numeric keypad, together with a bitcoin account at the server. No need to do any fancy GSM-audio hacks.

GSM networks only support well certain sound frequencies, but I'm sure it would be easy to encrypt digital 0s and 1s when using the correct frequency.
This should not be very difficult actually.

And BTW, this is an awesome idea.
Even if they censor the internet (which is unlikely), we will still transfer bitcoins over phone.

It is not "frequency". GSM use very lossy codec (as low as ~6.5kbit/s). Depends on which provider you use, and which circuit it takes, it may transfer over some other VoIP networks. You cannot expect any reasonable bandwidth / latency doing the "encrypt digital 0s and 1s when using the correct frequency" thing.

Sending with SMS is the only sane option.

Actually, not only that. The codec they are using only works on low frequency range (11 Khz or something), and the codec is specifically tuned to compress human voice best. It will not carry very high or very low tones properly.
So if you won't use correct frequencies, you will fail.