For most 'alerts' or notifications the lack of a response may acceptable,
and most of the email2sms solutions don't provide receipts, thou using a
modem directly you should be able to configure it to request receipts -
although that in may only be a receipt that the message was received by the
carrier, and not the handset. Some of the receipts we see when sending via
SMPP or Telecoms new UAS service (SMPP replacement) are 'number unreachable'
(bad number, or blocked off-net number), 'not received' (handset was off for
too long so message expired), 'received', 'no funds' (for prepay) amongst
others.
On 4/17/07, Gerard Creamer
Still relies on the txt message getting sent by Vodafone though, and as there's no ACK on a txt it's not guaranteed, but has been fairly reliable over the years. The SMS modems seem to die after 3 years, but apart from that it's been great :^)