I’ve been trying to get a 7945 with SIP to work with Asterisk and it just doesn’t want to register. Turns out the SIP load of 9.2.1 is broken, at least for asterisk. I’ve reverted to 8.5.4 and it seems to be working now.
I figured this out by downloading the log from the phone, finding : Error: cc_cfg_table is null and googling for that. No one comes right out and says it’s broken but everyone having problems is running a 9.x version.