Question about selling phone and using another phone
So I was planning on selling my 3gs and buying a 2g or old blackberry but the when I called att they said they would have to change my plan if I did that because it might not work because of the different data type or something and it might reset my upgrade date. Which they will not be able to fix. So my question is do I really have to call them if I switch to a blackberry or 2g or any cheap used att phone if I just pull out my sim card and use it in any cheap phone I can find until the new iPhone come out. Any help would be greatly appreciated.