A new Arduino shield is out for GSM (Cell Phone). It looks pretty neat TILL YOU SEE THE COST! Its almost 70 euro, which is like 120 US dollars. For that much I can get alot of stuff and just tap into a landline…better yet, do one of the hacks for a WRT54G and use WiFi.
http://arduino.cc/blog/2013/03/11/dive-into-the-new-arduino-gsm-shield/