Seems like the iPhone will benefit from an external GPS module somewhere around February. A GPS device to go with the preinstalled Google maps application is already in the works with a real prototype already available.
This is how the final module will look like
You can have a looksy at the device and how it works along with its custom application. In order to put the device into use you do have to have your iPhone jailbroken so that you can install the third party application that gets the GPS coordinates to Gmaps. You can learn more about jailbreaking and third-party applications in our dedicated article.
The GPS receiver module is produced by Part Foundry and is based on the SirfStar III chipset. Expected retail price is USD 89, which sounds like a good bargain. Here is a real life video of the prototype in action: