My wife has a Street Pilot III which seems physically too big plus the cubby opening (at least in a sedan) seems like it will restrict any view of the screen. But maybe it'll work. Time to yank that phone! The nice thing about the SP III is voice prompts so you don't have to keep one eye on the display all the time.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD