Hello to everyone

I have my Iphone for about 3 months now.
Im using it on Vodafone UK.
I was using software 2.0.2 and later 2.1 with Gevey Sim Card unlocking.
It was working just fine for more than a month.
I use internet all the time with voda.
Then I decided to update software to 2.2 and use Yellowsn0w.
Since I did it, phone works great, no issues with reception, but...
When I use internet in my Iphone it just stop after 10 - 15 minutes.When I switch to GPRS it works fine all the time,
When I use it in 3g - 10 minutes and its gone.Safari says 'Cannot connect because server stopped responding'!!
I change to gprs and 3g in a second, and it will start again for 10 minutes.
It looks like network is disconnecting me from internet!!

So I just wanted to ask , if anyone using Iphone in Voda UK and use internet all the time.
Im not sure if the problem is in 2.2 software or yellowsn0w??
On previous softwares( 2.0.2 and 2.1) it used to work absolutely perfect!!

Please help!!