If you are not on 8, don't bother with the J series. I've got a J179 on my desk and I want my 1608 back. Although some Avaya documentation says the J series is supported on 7.1, there are a lot of "gotchas." For instance, once you program a button, you can't re-use it. You can delete it, but you cannot program another button in it's place without completely removing the user from SMGR and re-building it. Audio quality is fantastic, but administration is a nightmare.
I wish we could stick with the 9600 series with H.323--they just work. Unfortunately "the powers that be" are hellbent on all SIP and are having us remove 9600/1600 phones from desks in favor of Equinox.