Thanks for the definitions!
I was wrong, the Treo 650 supports EDGE so if you want faster communication TIM would be better, unless you have EDGE with Wind too (not so widespread, but present). Anyway I think it won't change too much. If you are staying in Italy only you can go with TIM and one of its data offers (they are listed on this site too, in English, national operators sections). If you plan to use it in other countries too, Wind is of course much better.