I'd totally recommend Simcom SIM900 module for that. There's no way to mess with stand-alone cellphones.
You can get Arduino SIM900 shields on Ebay for 20-30€, way less than any mobile phone. Easy to control with UART AT Commands.
You can use "SoftwareSerial" library to aquire multiple sets of UART.
Here's everything you need to know to get started:
**broken link removed**
There's also SIM300 series and Siemens TC35, but these have a lot less documentation and are bit more hard to come by in single quantities. I recommend SIM900 if there isn't any particular restraint.