SMS etc

Hello all,
I apologize if this is deemed off topic, but I think there is enough
content to warrant the question.
Some time ago there was a lively discussion about SMS paging and the
providers for that in relation to emergency operations NMS paging etc.

Who can point me in the direction of the still serving providers and
maybe give some color commentary on the SMS to SMTP or other paging
methods many of you use to provide the paging of engineers?

Please reply off list and if there is any interest I will summerize back
to the list.