we recently upgraded from 6.x to 7.1.3 and then upgraded the 797X phones firmware to the latest images. After the phones upgraded, they would not register to cucm if they were remote. Locally on the LAN, it was fine. The phones were online at the remote site, trying to register to CUCM, but would fail, then go the SUB, then SRST and keep cycling over and over. We ended up backing down the firm two versions and the phones were fine then.
Id say this is ok, but we now have 7975 phones and 7916 expansion modules. They require the latest firmware to work. I have a TAC case open but was wonderin if anyone else has had issues.