Latest jailbreak doesn't have an unlock at the moment. By all accounts (at least) o2 will unlock for free tho.
As for PAYG, I'm not sure how they work in the US but pretty sure it's not as easy as in the UK. Data will still be very expensive tho even with a US sim, they don't seem (again) to be as good as us in the UK on this front either.
I spent about £250 on my phone bill for our wedding trip tho, had to ring and text much more than a normal trip, so hope you find some solution
Well I guess it's all relative but after a quick search I found
MrSimCard who specifically market a 15/30/60 day sim card, free US calls, free US and International texts, and the smallest (15 day) plan comes with 50mb of data. Depending on needs (ie just checking your email and the weather forcast) then that might be sufficient. All in it costs $80 give or take.
International calls are a bolt on and purchased in units of $10 which gives you a pin to call a special number which forwards you onwards (bit like a normal International call by the sounds of it). I looked at the tariff and calls are .2c a minute so get some bang for your buck and noticed it does come with a $1 free (50 mins) with the package too.
If more data roaming needed it's $12 per additional 50mb however you can get the 30 day sim for $100 and get 150mb so if you think you're going to use a lot of data then would be better just to get that.
I guess it depends how much you really want to get online and with your own phone but you could get your sim, 150mb of roaming, free USA calls, free texts and 17 hours of International calls for $120 which sounds fairly reasonable to me in the circumstances. Obviously if the exchange rate starts to improve again it'll start to look an even sweeter deal.
It also looks quite reasonable when you compare it to the above suggestion of taking a laptop as unless you're dvc their in-room web access is $10 a day though granted it's a 24 hour timer so you could wrangle that so as to not need it every day, but still.
I'm also positive I've read that you can buy sim only's from ebay for like, £5-6 quid and then get a bolt on package direct from AT&T USA for like $70-80. I'm sure if you found yourself a reputable ebay seller you could ask them for advice on that, they're specifically selling them to Internationals for that reason so they're sure to know all the options available.
As I say though, I've never tried this first hand myself, but it all seems to look a fairly commonplace practice so think it just boils down to how much people are prepared to pay for the convenience of having their iphone and wifi.
