Hi,
I've over 10 years experience with Microsoft.net and C# development, and have been developing for Windows phone for the past two years now.
I can deliver this app for you without difficulty. Most unit conversions are straightforwards and can be done to high precision. Currency conversions are a little more difficult as the app will need to get exchange rates from the internet. Most providers of this information are paid-for services, but I have used Yahoo! Finance in the past to get this information using their free and open interfaces, so I would propose using that to get exchange rates as each conversion is requested.
Your screen mockups look fine and quite achievable - in addition to the pivot/panorama interfaces proposed, I'd recommend we add an index page as well, so users don't necessarily have to swipe through up to 9 categories of conversions to find the ones they want.
I'd also suggest we make the software stateful, in that it'll remember the last conversions and units they did, so when they reopen it, it'll have the previous units preselected - that way if they use common conversions, they won't need to reselect it each time?
All my code is consistent with Microsofts design and style guidelines, fully Stylecopped and xcommented throughout. I'd give you all source code and the deployment package, so it should be plain sailing for you when you submit it to the Windows Phone Store for release.
Best regards,
Chris
PulseLab Ltd (UK).