There are a load of us going to the States for three weeks in summer, I have an iphone with O2 on a contract, whats the cheapest way of calling my friends in the States & calling home, do I just get a bolt on pay what the going charge is, or are there companies out there that rent phones with cheaper calls, or can I get a SIM card that allows cheaper calls or something along those lines?
Anyone have any experience of this?

Wi-fi + Skype

I was in California for three days in January for business, bill was well over £150. Glad I don't pay it.

Maybe a skype app and find a wifi spot.

Would I get charged for using internet access for Wi-fi?

No, well aside from the cost of the wi-fi access. Find a Starbucks or something with free wi-fi and you're good to go 🙂

cheapest way in the states would be to pick up a cheap pay as you go phone. They start at about $10, and for that some even have $5 credit included. Just remember that in the US you get charged for sending AND receiving calls and texts.
If using your iphone, you wouldnt be charged anything for hooking up to a wi-fi network, and that would work with skype.

iPhone automatically disables data roaming when your abroad. You can re-enable it but you better have deep pockets.

free Wifi acces is pretty common.

If you just want to call in the States, go to Walmart and you can get a pay as you go for $35 this give you a motorola phone and lots of mins that you can top up with your credit card.
I also us my O2 which roams onto most networks and its not to scary to call home or us it there.
Cheepest way to call home is a Phone card and a landline