Susan Mackay, VK3ANZ has developed her Maidenhead app for iPod Touch and iPhone which calculates the distance and bearing of another location from your present position. "Great Circle" distances and bearings are used. All bearings are "true" (not magnetic).
Both locations can be entered as a Maidenhead grid reference, latitude/longitude coordinates or via an interactive map. Where supported by the device, the local position can be set by the GPS.
Maidenhead coordinates can be entered as 2, 4, 6, 8 or 10 character values with corresponding accuracy in the conversion to latitude/longitude coordinates. Conversely, the Maidenhead value can be calculated to the same levels of accuracy (the initial default is 6 characters).