We are looking for a company in North America as a provider to transfert "data" signals, which is 1kb long, duration of transmission = 20 to 30 seconds and average of 100 signals per month, per users from IP to a PSTN. It is alarm system signals that will be sent via cellular (GPRS/TCP/IP) to an IP server. And the final destination will be a modem that use PSTN Network to receive the alarm signal (an alarm central). (we know that an IP receiver at the alarm central will be great but it is not all the alarm central that have IP receivers. And few of them charge 5 to 6.00$ per month to use their IP receiver. So, we want to avoid this)
Few peoples call that in VoIP market "short calls", but, it is similar but use "data" instead of voice over IP.