We've found other interesting behavior in email-to-SMS services using it for alerts (this is in the US):
Verizon: will deliver all messages typically with low latency.
AT&T: Variable delivery latency and they have some sort of rate-limiting where if your system generates 10 alert messages within a short period, they queue them up for a couple of hours!
Inmarsat: Fast consistent delivery but they have an undocumented rate cap that when reached results in all (all!) messages being black-holed for 30 days. There is no way to reset this state. The cap is something 150 messages per month or 5 per 10 minute period.
Verizon: will deliver all messages typically with low latency.
AT&T: Variable delivery latency and they have some sort of rate-limiting where if your system generates 10 alert messages within a short period, they queue them up for a couple of hours!
Inmarsat: Fast consistent delivery but they have an undocumented rate cap that when reached results in all (all!) messages being black-holed for 30 days. There is no way to reset this state. The cap is something 150 messages per month or 5 per 10 minute period.