Outgoing calls, sometimes
major US carriers have reported a bug on the iPhone 4S that occasionally mutes outgoing calls for users.
Apparently, the bug is down to a driver issue. Users, however, found a few workarounds such as switching the speakerphone on and off, plugging and unplugging headphones or activating Siri.
Apple hasn’t responded as of yet, but it is expected that the bug will be solved in an upcoming update.