I had a look at the MBK floor that Fio mentioned, lots and lots of choices. BUT they were quite expensive compared to the phone you can buy in NZ, so I didn't replace the one I got water logged (my drink bottle leaked in my bag). Have a look around at home first as there are some very good deals out there, and get a good idea of how much you could get one at home before buying one in Thailand would be my advice.