A couple of months back, my colleague James Simmonds wrote about a free Microsoft Office SMS Add-in (MOSA) which allows the sending (but not receipt) of text messages from within the Outlook 2003 client (in this context, SMS is Short Message Service - not Systems Management Server). I finally downloaded MOSA this afternoon and it looks good.
MOSA can only send messages using a GSM mobile handset that supports the Protocol Description Unit (PDU) standard. Initially, I attempted to send a message using a standard modem (without success - generating a "the modem does not support messages in PDU format" message) but once I paired my notebook PC with a Nokia 6310i via Bluetooth, everything jumped into life.
For anyone wondering (as I was), what exactly the PDU format is, I found some further information about SMS and the PDU format as well as a PDU string analyser and converter.