Installing and running apps off of the SD card is something that Tmobile has been working on. The phone will say "Low on storage" and then it'll go away, first of all, the Android Market takes up A LOT of space, I'm up to 24MB from the market, anyways, when the market's cache memory gets too full and causes your phone to promt that its low on storage, android automatically clears the cache memory fo the market. There is no way of doing it manually but atleast android recognizes that the market's cache memory is outta control.