IPhone 4s, iOS5.1, AT&T Call waiting turns on by itself - and if on Google Voicemail will not kick in. To turn on AFAIK one must have a cellular connection then access settings>phone>calls>call waiting>on/off switch. I have never turned on this way, only access to turn off. I would suspect there is an app that is turning on call waiting. The only one I can think of is Google Voice or GV Phone. Or maybe there is a shortcut I am accidently selecting? Anyone else ever experience this?