For those who are using a ad-hoc via laptop and not able to access internet all of a sudden in your iphone,pls check out the following.(for windows 7 using mcafee)
1.Reset ur mcafee firewall settings to default
2.Go to Ports and system services in firewall settings
3.open following ports-143,137-139,common operating ports,3389,443,80
4.create a new ad-hoc and try again(FOR NORTON AND OTHER USERS,pls refer to ur respective providers for similar ports and authentications)
For those using two or more iphones/other devices but not able to access internet in only one iphone,check out the following.
1.Turn wi-fi in iphone off and again on
2.Go to the desired wi-fi u wanna connect and connect
3.After connection is established,press the arrow in the right corner of the selected ntwrk
4.Click "FORGET THIS NETWORK"
5.When done,CONNECT AGAIN.SHOULD BE DONE.