Is there any web service that provides something to make phone calls? Let say I want to build one site where people can make phonepranks. I enter the number of my friend and when I submit the form, it calls him with a message like 7 days. Or like google does with its 2-step verification. When you don't receive a message google gives you the option to call you and give the code. 
Is there any web service to make phone calls like Google 2-step verification?
webapp rec
I just found it. It's called hoiio and it works almost on every country. It's affordable and easy to implement.The other options were tropo, pilvo ( I couldn't make them work) amd twilio (it doesn't work for my country).