Ive used this app for a long time and it is invaluable. Ive used it to communicate with my wife, to clarify something when Im shopping, getting somewhere, etc. It is frequently updated for function and seems to stay up with iOS changes. Its probably not for a tourist as it is rather expensive and more extensive than required. However, I would recommend it to any long term resident of Thailand.
TonyCr about Talking Thai <> English Dictionary+Phrasebook