hello ,

A way exists to send messages between movable telephones totally gratuitous. For we needed eight terminals and SmsCoop.
Some operators do not receive by the lost calls, case of Spain, reason why much people use this advantage to communicate ( that has not done a lost one).

SmsCoop, following McLuhan and its phrase “the means is the message”, uses the network to send information through lost calls.
The program uses four emitting telephones and four receivers connected via bluetooth to make the communication, acting one of them like “masters” and the rest like “slaves”.
Each telephone is able to transmit in each lost call 4 bits of information, being been in charge the receiving “masters” to conform the message.
Slow and complex to communicate, but totally gratuitous way (so far).
If you want to use SmsCoop with other seven friends it's available only for 2nd edition because it needs a new binary python extension phone_ext.pyd (source is not available so it's impossible to recompile it for 3rd phone

PS : phone_ext provides 3 functions (one extract from old callstatus.pyd from the same authors (Aalborg university)
Code:
import phone_ext

phone_ext.CallStatus() # return status call
phone_ext.HangUp() # hangup call (different from telephone.hangup()
phone_ext.LastCall() # return phone number of the last call even not responded !
links :
phone_ext.pyd for 2nd only
SMSCoop site
Installation guide
SMS Coop for 2nd FP2
SMS Coop for 2nd FP3