Originally Posted by Nikhil

Lol...what.The iphone 5 and mini come with iOS 6 then how did it get resolved.i don't think the factory updated phones have problem

What he means is that the recent iOS 6.0.2 update that was only available for iPhone 5 and iPad Mini fixed a WiFi issue. iPhone 5 and iPad Mini shipped with 6.0 and there have been 2 updates since (6.0.1 and 6.0.2).

Previous devices like the iPhone 4S, iPad 3 can only upgrade to iOS 6.0.1.

This problem seems to be happening for most of them after iOS 6 update. Reseting the network could give some better solution. Follow the steps given below to reset your network

Settings->General->Reset->Reset Network

You can see a better difference in internet speed after performing this. To ensure it have a speed test from http://www.scanmyspeed.com/ . Good luck.

Originally Posted by fredpete

This problem seems to be happening for most of them after iOS 6 update. Reseting the network could give some better solution. Follow the steps given below to reset your network

Settings->General->Reset->Reset Network

You can see a better difference in internet speed after performing this. To ensure it have a speed test from ScanmySpeed : Check my Internet Speed . Good luck.

...or better - install IOS 6.1 which has resolved ALL of my wifi issues.

I'm also having 3G connectivity issues after taking the 6.x.x (now at 6.1.3) updates. Prior to the 6.x.x updates 3G speed was good. I tried resetting the network settings as mentioned above. Seems to help for about 30 seconds. Occasionally things work OK. Went to the Apple store and they replaced the IPad and the Sim card. Same problems - I get a message saying "Unable to activate the cellular network". The signal seems to pulse between 1 and 3 bars over a few seconds. The Iphone works fine accessing the same 3G carrier. The signal is a bit weak but wasn't a problem before the update and Apple say I can't go back to a previous revision - too bad I wasn't doing regular backups.
Any other ideas? I think it is the IOS but of course the genius's don't know anything about it.

Have you tried resetting your router or have you tried a different router. Sometimes that has been known to help.