New Englander:
The 4 is not being replaced because it was a failure. In fact, the DIAD 4 was the first device of its kind. It has a cellular radio, GPS, 802.11, Bluetooth, IrDa, etc.
It was the first device to incorporate all those features.
All hardware reaches a life expectancy, and the DIAD 4 will begin reaching its in 2010 or 2011.
Electronic parts get obsolete and have to be replaced. You can't buy the parts any more. DIAD 5 will be replaced 5 or 6 years after its introduced. This is by plan.
I'm glad that someone in Corporate plans that far ahead.
P-Man