Apple pulled an update for the iPhone operating system after multiple users had reported problems with their phones.
Scores of customers experienced dropped cellular service so they couldn't make calls. Some said the fingerprint reading Touch ID feature also wasn't working after the update.
"No service on my iPhone after iOS 8.0.1," said one Twitter user. "DO NOT UPDATE," said another.
The issue appeared to be affecting iPhone 6 and iPhone 6 Plus owners the most, according to media report on Thursday.
Apple said in a statement that it had received reports of the issues with the update, which is called iOS 8.0.1, and the company was "actively investigating these reports" while pulling back the iOS 8.0.1 update.
Trudy Muller, a spokeswoman for Apple, said customers can still use iOS 8, which was released last week. Apple will provide information as quickly as possible.