GB Grid Converter
GB Grid Converter is a free App by GPS Log allowing you to easily convert between British National Grid References (i.e. OS Grid Refs) and Latitude, Longitude coordinates (both OSGB36 and WGS84 are supplied).
Then, easily view the converted coordinate in the iPhone's Map app, or send it to GPS Log. Or copy to the clipboard using the standard iPhone functions.
Fuzzy parsing logic allows you to input coordinates in a variety of ways, like "TQ 30267 76930", and "TQ302769".