@sarond - The extension is 521 and the hot desk agent ID is 5*21. Yes they have the same COS with hot desk enabled. They do show in the SRC just the status never changes from IDLE. Yes, all the 53xx series phones are working normally, just the new 69xx phones which are all hot desk users. I did try a 69xx phone with a non hot desk user and it worked, so I think it may be hanging up within the hot desk users ID's being different than the extension itself?
@doncarlyon yes they appear in the SRC but never change status from IDLE during a call.