find nearest places in iPhone

Answer 1

It's true, there are a lot of reverse geocoding services out there (Google, Yahoo!, GeoNames, etc.) to convert from a lat/lon pair to a street address.

But if you have lat/lon pairs in your database already, then I don't think you ever need to convert to a street address. Calculating distances is much easier if all your points are represented by lat/lon, you can use the Haversine formula.

And in fact, if your database natively supports spatial types (for example, MS SQL 2008 appears to), then you can push that calculation into the database layer and not have to worry about it. That seems like the right approach to me: have your iPhone app send lat/lon to your web service and have the database calculate the nearest points-of-interest.