On a side note, Dougy83 is correct, you can get GSM modules from places like SparkFun / Ebay, SIMCOM (SIM300 etc) and Telit breakouts are quite popular. Try and find one with a power circuit if you can as you will require a 2-3A supply if you ever want to connect to GPRS as it will peak at this level (module dependant).
If you wish to automate something like sending an SMS to a few phone numbers, then you will need to interface one of these modules, or a mobile phone, make sure that the SMS supports TEXT mode and not just PDU as PDU encoding is a pain for a beginner, grab yourself a microcontroller and you may need some level shifting and hook it up to the GSM module / phone and then grab yourself a copy of your phone or GSM module's AT Command set.
HTH
Wilksey