I've co-developed an app for the Windows Phone platform the gives romanized transcriptions from english to thai. There are a few alternatives for android and iOS users, including the very good Thai-Language App for iOS, but non for Windows Phone users until now. Here is the link to the app
http://www.windowsphone.com/en-us/store/app/english-thai-westernized-dictionary/027c0473-e2f5-4705-a853-a660b88f9efa
I'd appreciate any feedback about the app. We are working on an off-line version that should be released in the near future as well as adding a speech function.