HTC Desire - Upgraded to 2.3 - MobileNetwork is often not working

[scsvel]

Hi all,
I am facing problems in switching ON mobile network. Recently I upgraded my HTC Desire to 2.3. And When I restart the mobile, immediately MobileNetwork is connecting and working fine. After some time, say 10 mins or If I used to get any calls then Mobile Network status is Checked only i.e. Mobile Network option is enabled, but it shows below Use Phone for data connection when Wi-Fi is unavailable.
If I re-start the mobile now, its working for some time. I don't know whats the problem.
From these things, I am sure no problems in my Service Provider AIRTEL INDIA. Whats the problem with mobile?

Anyone please help me...