Hi dz,
I don't think that this is common, but I think it can happen. Questions, -
do you have the phones defined as locals or remotes?
do you have a re-register time set in the phones themselves?
We have mainly aastras and snoms deployed in our customer base and the problems we see are mainly with the newer 5xi aastra units. They tend to be OK as long as they are regularly restarted so, on most sites, we have them automatically restart every night at 00:00. However, from time to time a phone will lock-up and sulk, whereupon it has to be manually restarted. Not good but just about acceptable. We have some big deployments of the older 9112 and 9133 units and they rarely give trouble.
We never have any technical problems with Snoms, the firmware is rock-solid. They do have issues tho' and these tend to revolve around their rather awkward usability, particularly for blind/attended transfer.
Lastly, we have issues with Siemens DECT units (mainly the C460IP ). Most of the time, these are great phones. They are inexpensive and have superb range for a low cost portable unit. However, if you get any glitches on your LAN (maybe a minor router or switch fault) which drops the LAN for more than a few seconds, the phone loses its registration with asterisk and it NEVER re-registers. The result is that it can continue to make outgoing calls but won't receive any incoming unless/until it is restarted.
Don't know if any of this helps.
Kind Regards
S