What kind of SIM card will I need for the Sony Ericsson W580i Walkman?

if it is locked, then u have no choice but to use att, but if its unlocked, then u can use any sim card u like. I don't know what sim card it needs, but as an experienced phone owner, my suggestion to you is to stay as far away from anything Sony Ericcson as you possibly can. I got the phone in November of 2008, around 5 weeks later the brain of it starts freezing and shutting down for no reason when everything else like the battery and the memory capacity is all at normal levels. So I take it into at&t to see what the problem was, and they send me to this ghetto-ish place for a refurb. So I get the refurb, and it brakes litterally THE NEXT DAY, I take it into another at&t, and apparently the pink one has been discontinued ans I have to be stuck with the ugly black and orange one. I get that one, and then like 8 weeks later the buttons stop working and I have to get another one, and the one I have now, the frieking front is coming off when I didn't even drop it or do anything!!! So for your convenience, I highky suggest nixing that phone. Have a lovely day!