Having issues with 3448 and Aastra phones loosing service. Unit show a memory issue, we reboot the 3448 and service restores. A month or two will go by and again the same issue. We have replaced the unit and the new unit is starting to do the same thing.
This sounds like a memory leak which is typically a software bug. What version of firmware are you running and have you checked release notes on more recent versions to see if this is a fixed bug? If you're running the very latest, consider rolling back to the most recent "extended maintenance" version.