IPhone 4s Wifi Problem - now on my second device and still not working..help

Question

I got my first iPhone 4s less than 3 weeks ago the wifi worked fine for the first week and connected fine without a problem. I then began to have problems where it would appear with the server cannot be found etc. Yet i had full signal on the wifi and my 3g works fine, i was quite fustrated reset my phone, and also my wireless I had no luck! I contacted my provider and they tried a few things I could join up to my wireless it would work and then would stop working after 5 or 10 minutes,  what they couldn't understand was my partners 3GS worked perfect and so did a friends iPhone 4 when they used the connection, previously I had an 3GS myself and it worked perfect with the wireless. My provider decided to send out me a replacement 4S I received this earlier on today, the Internet worked fine on my wifi and then the same thing has started happening again, I have reset the phone a few times and works okay for 5 or 10 minutes (like now as I am typing this) but then again comes up with the same message with cannot connect to the server, even though I have full bar on the wifi signal and sat next to it.
I am stuck at a dead end and unsure on what to do I use my phone for everything and I find it frustrating that I cannot use my Internet on the phone properly and I am already on my second handset.
I was wondering whether anybody could help me out with this as I just don't know what to do
Any answers/advice would be much help and greatly appreciated.
Many thanks

Answer 1

I have the exact same phone as yours but the thing is, connecting to wifi and 3G and surfing the net with my iphone is fine. when it comes to updating and downloading apps. it took years to do it!