I haven't seen anyone using the solution we have here - bluetooth. The monitoring server has gnokii, the blueZ stack and a Belkin bluetooth USB dongle. Nearby is an old Nokia 6310i (permanently connected to its power supply) paired with the monitoring server and able to send SMS to a preset number.
In /etc/nagios/misccommands.cfg is the following section:
'notify-by-sms' command definition
command_line /usr/bin/printf "Svce: $SERVICEDESC$\nHost: $HOSTNAME$\nAddr: $HOSTADDRESS$\nState: $SERVICESTATE$\nInfo: $OUTPUT$\nDate: $DATETIME$" | /usr/bin/gnokii --sendsms 0798XXXXXX
Just add "notify-by-sms" to your callout contact in /etc/nagios/contacts.cfg and you're set.
When the escalation state is triggered, nagios sends the command to gnokii which sends the message via SMS.