The 2420 doesn't really impress me.. About half of the display could be used a lot better. But button labelling from the IPO is nice though! Unfortunetelly it's not possible to rename the buttons.. (until 3.0)
The 6408/16/24 is actually a nice phone to use. But Avaya should put some work into everyday use. The display should have more "dynamic" menues.. Those who have used 2030/2050 know what i mean!
Keep away from 44xx, it's just crap! Buttons getting stuck, and it's really cheap-looking. The 44xx phones are now removed from our market due to poor quality. Also it only supports mu-law companding, which is a bit of a problem here.. If the CO-lines are A-law ISDN2 a Uni BRI module is necessary. On an A-law ISDN30 there's no chance!