What all modern smartphones lack is a good gps module. The one that comes embedded in them is so slow and has such a delayed response that they're truly useless in their function.
In Kerala, on a rainy day, first satellite lock is achieved on a nokia n900 in 2 minutes. After that we get locks in under a minute.
With the motorola gps, the n900 achieves initial satellite lock in a minute subsequent locks are achieved in 3 secs. Using this device vastly increases the performance of all the navigation and mapping apps in the phone. The acceleration and speedo check works like a charm with the sirf3 module. The internal gps resulted in a lot of errors in the results of these apps. I got my gps module for testing from mobilefun. I did see some different models for gps recievers in the bluetooth accessories section like a keychain styled one and a cube-like design as well. But the SIRF-3 turned out to be quite a high performer =)
This device also comes with free motonav service that lets you use navigation on almost any phone even java phones!