I don't know this for sure...but, I don't think your current plan is tied to your SIM. I'd go to a Cingular store w/all 3 phones so you can show & tell them the problem. They "should" give you (as in gratis) 3 new SIMS. I thought our SIMs were just our account info and any contacts etc that we store on it AND, of course, the key to the network. The SIM locked thing is when your phone is locked and can't use another service provider's SIM. But, if you have a Cingular phone that is SIM locked, you should be able to put a friend's Cingular SIM in and be OK. It'll just ring/answer their phone number now. You'll have no luck with a T-Mo SIM though. See the difference?
I just bought a Cingular 3125 (not tied to any plan) and not from Cingular (got mine off of eBay). It's came locked. My Cingular SIM worked fine. Our T-Mo chip got nothing. I unlocked the phone last night and now both SIMS work just fine in it.
I bought my MPx200 on eBay about a year ago and it came with a SIM but from the other side of the country. I went to my local Cingular store and traded them for a new 3G card. Since that time, I've also purchased the MPx220 and my current i-mate (all off of eBay). The SIM that came with the 220 worked just fine until I flashed the ROM and then I started having connection problems. Cingular replaced my SIM three times before I figured out the new ROM was the issue and I flashed another over that and it's been good ever since.
My i-mate just quick "connecting" one day. I'd done no tinkering, it started out the day just fine and then <BOOM - like yours> it quit! However, I never got the "Unable to complete the call as dialed" message. Mine was just continuously "searching" so I could not use the "phone" part of my device at all. I took it into the store, got a new SIM and went merrily on my way.
Now, my plan is not a grandfathered plan that I'm clinging to which sounds like yours might be. That's the only thing that concerns me with your story. I'm sure they'd waste no opportunity to try and get you onto one of their newer more expensive plans as the only "fix".
Bottom line...a screwed up SIM should be replaced by Cingular at no charge to you. I wouldn't go in acting like they'd be doing me a favor to give me new SIMs. I'd go in with the attitude that they messed me up and they need to fix it. It's also been MY experience whenever something is wrong, Cingular's first impulse is to say go to a store and get a new SIM! If that doesn't fix it, then they really don't have much else to offer. Know what I mean?
Now, for your P.S., can the MPx200 accept newer Cingular (or, non-Cingular) SIMS if unlocked. The answer is YES! My MPx200 runs on the most recent 3G SIM from Cingular that normally is in my i-mate (the SIM I just got a couple weeks ago as mentioned above). It runs on our T-Mo SIM without a problem too.
Likewise, your older SIMs *should* work in newer phones. The caveat being that 3G thing. I'm not up to speed on these things either, but in the back of my mind I have a vague memory that there are some newer phones that must have the latest SIM. I remember zero details about why though. Easiest way to find out is to try your SIM in a newer phone and see! In fact, I'd do that while I was at the Cingular store. Or, is it since it's an old ATT SIM it won't work? Hmm, again, I don't know for sure - but, I'd be eager to find out.
Road trip!!!!!!!!!!
Good luck!
ohhhhh, also, check out this thread:
http://www.mobilegadgetnews.com/index.php?...ost&p=56965lil14kid says there is a $50 family plan that maybe you'd be interested in finding out if it's so!
Devices: T-Mobile MDA (Cingular SIM), i-mate SP5m (sitting in a drawer at the moment while I attempt to migrate to PPC permanently), Cingular 3125 (unlocked and in use on T-Mobile), Motorola MPx220 (retired), Motorola MPx200 (retired)
Accessories: Plantronics Explorer 330 & 2G Patriot Micro-SD (use w/MDA), Kingston 2G mini-SD used in SP5m, Plantronics Discovery 640 & 2G San Disk micro-SD (use w/3125), Jabra A210 BT adapter + Motorola HS805 (retired)