"if it fits, you must..... use it..."
if it has any info on it from the previous phone, i would format it using your pc first prior to putting it in your phone... or you could place it in your phone, boot into recovery, mount sd card, and erase/delete that way if you do not have a card reader... i suggest this just so there isn't any conflicting data/info from previous phone...
EDIT - 2G? not sure if that's big enough... you could try... can't hurt...