If you mean updating the software, the reason for this is because things change. Landmarks change and roads. Updating gets all the new info in so your GPS can work properly! This also helps you access any new cool features.
Most GPS devices update their software automatically, so users don't need to be concerned with upgrades.
No service required, you simply use gps. Updating the maps can be quite expensive, checkout the best value formney upgrade before purchasing the GPS unit.
If a GPS system is leading you to non-existent addresses, one should definitely have the system updated. These GPS devices are very accurate now, but do remind owners of the need to upgrade every so often.
under the passenger seat
No. You would need a separate GPS receiver and GPS software (i.e. TomTom) on your palm device to decipher the GPS receiver's signal into information you can use.
You would need to down load an app for it.
To hook your GPS up to your speakers you would need a GPS systems with a head phone jack. If you have a head phone jack on your GPS you can use the same plug from your iPod with your GPS system.
Almost all new vehicle above middle class or economy, would have GPS either standard or as part of an optional upgrade to the vehicle. Many options exist for after market upgrades as well.
Nextel GPS information can be found on the Nextel GPS website. The website will have all the information that one would need. Nextel GPS is a phone software.
It would be ideal to call the local attraction sites and inquire about needing marine gps snorkels. They may have the equipment you need onsite for your snorkel.
Removable GPS unis are convenient because they can be easily replaced if broken or if an upgrade is desired. Some people prefer the aesthetics and integration of an installed GPS unit, however.
If you are planning a family vacation and need a GPS to guide you on your way, then I would suggest the brand TOMTOM since it provides cheap and effective GPS systems.