Make phone calls with Arduino

I want to use an arduino to make calls on a cell phone. I've done some digging around and I've seen a lot of complicated or expensive solutions using shields, multiplexers, pure data, asterix etc. Any idea what the simplest way to get this done is? I haven't decided on what phone i'm going to use. Something cheap and easy to work with. At this point my best solution is to just run leads right to the buttons on a cheap phone. Any one have a better idea?

Save yourself the trouble of hacking a good mobile phone to get a botched solution. Try this:

http://www.libelium.com/tienda/catalog/product_info.php?products_id=59&osCsid=8bda9122d06c5a8ce047b3c7467df72a

They are cheap and simple.

They have a basic tutorial here:

http://www.libelium.com/squidbee/index.php?title=New_GPRS_module_for_Arduino_%28Hilo_-_Sagem%29

Cheers