I have a 4s using AT&T net 10 sim but I switched to t-mobile net 10 sim so I can get my unlimited data back. But how do I know if my iPhone is unlocked. I did the transferring to a different sim activation already but when I use my t-mobile sim I try to make a call and I get a busy tone but my it's says t-mobile on my status bar. and my AT&T sim is deactivated so I can't use that one. I used that imei site but under sim lock it says unknown.