Apple has released a software update for iPhone 4S users, after U.K. and European cell networks warned iPhone users to avoid the latest iOS 6.1 version.

iOS 6.1.1 is delivered to iPhone 4S only users to fix a bug in the latest iOS 6.1 platform release. iPhone 4S users complained that the latest upgrade caused cellular and 3G networking to suffer.

The latest patch is avaiable for download over-the-air. In the release notes, Apple says the update "fixes an issue that could impact cellular performance and reliability for iPhone 4S."

Earlier, Vodafone sent a text message to all its customers warning that they due to the installed iOS 6.1 iPhone 4S devices, they "may occasionally experience difficulty in connecting to the network to make or receive calls or texts or to connect to the Internet,"

Three Austria sent out a similar warning.

Wi-Fi related problems continue to plague some customers who first upgraded to iOS 6. The iOS 6.1 update fixed the problems for some users, although not all.