I used to do this back in 2005. Forgive me if something has changed in the intervening years. There was a rate limit for receiving and sending SMSes via the ha

I used to do this back in 2005. Forgive me if something has changed in the intervening years. There was a rate limit for receiving and sending SMSes via the hardware approach. My experiments yielded 1 per 20 seconds iirc In the end my implementation purely received via hardware and exited via a bulk SMS provider like clickatell clickatell at that stage allowed big users to set the 'sender caller id'. This was loved by spammers unfortunately so the providers became much more cagey about allowing that feature.