After a (admittedly possibly sizeable) investment you could send free, simple, international, text messages, from a mobile device, forever.

The idea is a machine that takes a number of pay-as-you-talk sim cards (maybe 16 or 32 would be ok), and communicates with the relevant mobile network as if it were 16 or 32 individual phones.

The machine has a little keyboard and text display. You need two of them.

The free principle is that calls are not charged for at all until they connect. When you type in your message and press send, machine 1 communicates with machine 2 in binary (i = one ring and hang up / o = no ring).

Certainly it`s going to be cumbersomely slow, especially with international call connect times. Also you might need some tricky error correction programming, especially as communication is essentially one way at a time. Certainly you could not make a product of it, as the involved companies would stop it somehow.

That said, mobile networks in the UK have do have agreements that allow their pay-as-you-talk customers to roam internationally, with no additional call charges except those incurred when a call connects.

also I reckon it`s something that someone a little more technically minded than myself could cobble together with readily available parts.
-- goatfaceKilla, May 02 2005

A SIM multiplexing thing http://www.casabyte...rver%2002.10.05.pdf
[DenholmRicshaw, May 02 2005]

If you used 36 phones, each one could correspond to a letter or number. No punctuation, but it'd be quicker than trying to use binary.
-- david_scothern, May 02 2005


Yeah. I`m not really clever enough with that sort of thing to say.

Whatever system you use would have to deal with internatiol connection times that could vary between 1 and (say) 10 seconds.

But yeah, machine 1 would know that machine 2 had recieved character 1 because it would hear the ring tone, so no problem with things getting out of order.

Som really strange things happen when you make international calls, especially from mobile networks, so I was thinking binary for error correction.
-- goatfaceKilla, May 02 2005


See link for SIM multiplexing technology.

You could set this up with 36 SIMs (apparently you can join them together so you could have more...) and use it to switch identities in cunning ways to convey information using the calling line identity.

The called party could see the identity of the calling party and could infer information from this. Something like SIM1 followed by SIM2 means "hello". SIM3 followed by SIM32 means "a" ... you get the idea.

It might be quite slow though.
-- DenholmRicshaw, May 02 2005


<obligatory> I wasn't aware they were enslaved </o>
-- ato_de, May 02 2005



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