removing the sim and RF question

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...

Without a sim the phone is probably scanning all networks

that's what I was thinking. And if this is true I just have to find out which one is the strongest in my area.. That would be pretty neat if that's what the phone is doing.

It would be a pretty easy way to find out which carrier has the best signal in the area ??

you can search the network manually by chossing the network selection, and then there is the list of network, and i think the best signal is whichever in the top (but maybe your provider is in the top, that will be the number 2).. maybe.. i dont know too..

i forgot which handphone that can search and sort by its received quality signal..

That is the emergency signal itself.. I think so. I don't think that the strongest signal is at the top of the list of network providers.. The top of the list is always your network provider. I use in Paraguay 4 network providers (don't ask why, je) and whichever sim card I use, always show at the top of the list the actual network of the sim car.

NO simcard > scanning all available BTS.
The bar shows the best reception.