add me to the list too. I was a long time E90 users and was never faced with this problem but i have had it with different phones with the same operator. I have been doing some testing I have activated the data and setup a continuous ping with a larger packets and left it running, also i have have launched the browser and gave it a big webpage to load with a lot of flash.

3G data connection is still activated and calls go through the odd one got rejected probably as I wasn't giving the phone a break lol.

I then force the phone to use 2G and with the same results

All below had problems.
Tmobile
Vodafone
o2

I did this about 10 times on each network. A few times data disconnected red cross and the phone rung. Other times straight through to voicemail. There has to be something setup or a fix for this as this is becoming a deal breaker for me as much as I love the phone not all my locations I am in have good reception.