A similar sounding set of symptoms from searching the forum is here:
http://www.geekzone.co.nz/forums.asp?ForumId=6&TopicId=11042
My phone, when idle just sitting on the coffee table in the lounge will at some point go into a mode that for all intents behaves just like flight mode. I stop recieving SMS messages or phone calls. If I pick up the phone to send an SMS or make a call I get an error for SMS saying the network is unavailable and for phone, I get the normal dialling, connected but nothing after that (no ring or anything).
Note that if the phone were in flight mode and I try to make a call I get asked if I'd like to turn flight mode off so it's not as if my phone has flicked into flight mode somehow.
If I am on the phone and enter my lounge it's still working fine. I have 2 bars of signal strength which is low (4 bars at other end of the house: Glen Eden area). I have had no trouble with 2 bars of strength in the past.
My wife's Tre0 650 nor my son's el-cheapo sanyo have any such trouble in the lounge.
Same applies to the Ak UNI gym locker room and down at the squash courts.
When I have entered a no coverage zone in the past where ther eis literally no signal, I get the correct icon on the phone showing no signal.
I think it might have started when I put in AKU2.2 but I can't be sure as I was not in this house at the time. I visited this house from time to time however and I never had the issue before. I can't be sure when it began because I also had a dead region of screen soon after getting this phone. The phone went in for repairs and came out with a new screen. Soon after this my company started to recommend the AKU2.2 upgrade hence I went for it.
The radio version is 1.12 so one thing I looked for was any sort of upgrade. Tellogistics say they have a later version but I have to take it in to them etc. I might have to do that unless someone has a suggestion. I already asked Tell;ogistics for access to the radio upgrade but they claim it is not allowed to be passed on. I am finding out more about this claim.
Any thoughts? I call this fault the "stealth mode bug" because it make the device worthless as a phone as I have to make regular test calls to ensure it's working.