phone call with an arduino

hi, scuse me for my english, i’ve a problem: i’ve to make a project of a domotics home, an i’ve to make a security sistem with motion sensor, that after they have found something in their range, connected to an arduino, make a phone call.
If anyone can advice me how to do it, thank him.

I think that many old standard modems with a serial port can be controlle with the standard AT commandset to dial a number.