can you only trade with other platinum players in the gts if you play platinum?
i don't think so; considering i can't use the WiFi rooms. but i went upstairs 2 the union room and traded some Pokemon from Pearl over 2 Platinum, and it worked fine. since my little bro has a DSi, i can easily trade over Pokemon via the union room. so i really can't say, but if u have a sibling that also has a ds or dsi, i would use the union room. hope it helps somewhat!