OK, I'll add my two cents.
1. I have two AT&T Cell phones. I keep AT&T because only them and T-Mobil use the GSM system. (Verizon and Sprint use CDMA)
The GSM is the system used worldwide except for Verizon and Sprint in the US. I've used my AT&T phones in Europe, however the cost is much too high. $1.29 a minute, unless you use their special plan, paying them an extra $5.00 a month, and then out of the goodness of their heart, they only charge you $0.99 a minute. Well I am long past my contract time, but one of my phones was giving me problems. Sure, AT&T will upgrade my phone for "free" but lock me on to another two years. Also, the AT&T phones are "Locked" which means that I can't use someone elses SIM card in the phone. OK, what did I do? I purchased an Unlocked Phone off the internet, removed the SIM Card from the phone that was giving me problems, put it in the unlocked phone, and Voila, everything works. All information still in there, because it is in the SIM card, not the phone. Next time I go to Europe, I will purchase a European SIM Card with a French phone number, put it in my unlocked phone and use that for making calls. I will place my AT&T SIM card back in my older phone and carry that just for incoming calls from the US.
2. Because I have AT&T, I decided I would get an AT&T Air Card for my laptop. Called them, and they sent the aircard, SIM card and battery. Plugged it in the USB port, and I could not get it to work. Called AT&T to see why. THEY HUNG UP ON ME TWICE. (Yes Twice). After trying to talk with their Customer No-Service People, one asked if I programmed the laptop with the disc. WHAT DISC? They told me that I have to load the disc, but they never sent me a disc. OK, they then said to go to my local AT&T store and have them load their disc. Well, the AT&T Aircard did not use a disc. The guy at the local AT&T store worked for two hours trying to get it to work loading the information with a Flash Card. Tried two different Flash Cards. Still could not get it to work. Went home, phoned AT&T and told them that I've had their aircard for four hours, and it does not work. Sent it back and yes, I got my money back. Did I tell you I had Customer NO-Service?
3. A week or so later, I went to Circuit City (remember them?) and got a Verizon Air Card that plugs into the USB port. Loaded the enclosed disc, followed instructions, plugged the air card only when instructed to do so, and Voila, everything works.
4. Because aircards have a "telephone number" I noticed I was getting Text Messages, (to the person who had this number before me) and I could not remove the texts until I had read them. Telephoned Verizon, and I figured I would have problems getting rid of the ability to receive texts, plus get rid of the charges. Easy. The Customer Service Rep told me that she was here to serve me, and she removed the charges, and fixed it so that I would no longer get texts on this aircard. For me, Verizon treated me good. I don't understand why they still use the CDMA system when their owner, Vodafone (Europe) used the GSM system. I told them that when they switch to the GSM system, I will dump AT&T and switch to Verizon. (Verizon says that CDMA is better, but what else could they say, that AT&T (and T-Mobil) system is better??)