I use ATT and travel internationally, so I am familiar with what you need.
If the old phone worked last time, then it does have the correct frequency bands for starters. However, if you don't remember using a pre-paid SIM last time, you will want to know if it's unlocked. If you are already 100% certain of this, great. You can go over there and purchase a pre-paid SIM at the kiosk and enjoy. Otherwise, the best way to determine if it's unlocked is to borrow a friends T-Mobile SIM card and test it out on the phone in question. If you can place a call with a T-Mo SIM on your old phone, this means it's unlocked. If not, simply call ATT's international desk for this service. 1-(916)-843-4685 Typically, they email you what is called a subsidy unlock code for your specific handset (IMEI number is required from phone). This can take up to 7-10 days, but I've received them for very new phones right over the phone and also overnight via email. YMMV.
I hope I can find an expert for this problem I am having. I plan to travel to Germany very soon. I just found out that my current cell phone does not have german capabilities, unlike my old phone which I used on my last visit a few years ago.
So, my question is, Can I take my old phone which used to be with Cingular and still has the Cingular Sim Card in it, take it to Germany and buy a german Sim card over there, or even over here on the internet ( I found some sim card sellers who claim world wide capability ) and then in Germany just start making phone calls ??
Maybe my train of thought is wrong but would that work ??
I think something about unlocked or locked comes to mind, would my old phone if the service with Cingular has been disconnected 2 years ago work with a different sim card or is it still locked ??
thanks for your time, hope I can get this figured out !!