NOKIA C5-03 Internet connectivity Problem..

[mdp]

I Have Nokia C5-03 bought before 4 months.
I use BSNL Prepaid card, 3G/EDGE enabled.

I am facing problem of not being able to connect to internet via 2G/3G reliably.

whenever I try to connect to internet, 7 out of 10 times it gives me message"
"connection not available.pls check connection settings".
Many a times after restarting the phone, internet gets connected.but not always.

I also own Nokia N73. But whenever I insert the same SIM card in it, it never failed to connect to internet, neither it has given me such problem in last 4 years.

In only In Nokia C-5 03 I Need to struggle for getting connected to net.

2 times I visited Nokia service center, but they have only formatted it and installed software to it and gave it back.

I have also installed latest version software to my handset from nokia site to fix any bug if it has any..

But it doesn't work..

what i need to do..?