Re: Tons of "internet access" data charges while abroad
On OS 5 at least, it would be options > advanced options > TCP/IP, then delete the info after "APN:". For example, you probably have set epc.tmobile.com.
If you are running OS 6, it will be the same general idea, but you may have to look for it in options.
You may be able to get away with just unchecking the APN Setting Enabled box, but I've seen it advised by another with a lot of experience in this that it is better to delete the apn to be safe.
If you find that your APN settings are blank, then I will be really confused as to what happened on your trip.