removing the sim and RF question

[dan409]

I was just wondering when you remove the sim card from your phone you can still make emergency calls right ???? Sure you can !

I have noticed that when I turn on my phone with the sim card removed I always get 5 full bars of reception.

My question is this. Where is the signal coming from? Is it possible that it is from another carrier. When I put the sim back in and it locks on to my carrier(at&t) I don't get nearly as strong a signal ???????

Thankis Dan

The reason that I am asking is that I have just moved and may have to switch carriers...