I've had Cingular service for the last 5 years. I ordered a new phone last year from the Cingular website (renewed contract on the same service plan) and the phone came with a new SIM card. But I just took my old SIM card from my old phone and plugged it into my new cell phone and it worked just fine, with all my phone numbers still in memory. What do I do with this new SIM card, which I never used? Did it come with all my information/phone number preinstalled? If I gave this SIM card to someone else, how do they go about getting a new service with it?

I apologize that my knowledge of SIM card and related technology is rather limited.

It is un activated which is fine, keep it just incase you need one ASAP.

-Vincent

Look at the 2 SIMs and see if the new oneis marked "64K" and the old one is "32K". I suspect that this is the case.

It is rumored that the new 64K SIM is branded with a carrier ID that can use the old AT&T and Cingular GSM networks better which would mean better coverage.

If this is true, then migrating over to the new SIM would be a good thing to do.

If you have a Nokia, the technique is to copy all speed-dial data into the phone's memory from the old SIM. Then install the new SIM into the phone and copy/move all speed-dial entries from the phone into the new SIM. The, call Cingular and have a "SIM swap" performed in their system. Note that you will have to read the new SIM's ID number to the agent with perfect clarity!

Although I used to store all of my directory in the phone, I now store it in the SIM so that when I swap SIMs with those of different countries, I get the carrier specific shortcuts moving correctly with the SIMs. i.e. My Tmobile USA balance inquery is correct for the installed Tmobile USA SIM and my Orange UK balance inquiry is correct when I have the Orange UK SIM installed.

I don't know what technique to use with different brands of phones.

Oh, to the OP: Cingular and other carriers send out SIMs that contain a fixed "ID number" and sometimes a few carrier specific speed-dial entries. None of the user's entries are sent out and the carriers have no idea what is in the users's SIM directories. And the user's number is never branded into the SIM. The carrier simply links the SIM ID number to the user's phone number/account in their system The rest is GSM magic!