In Canada, Rogers has just started selling the W580 with 8GB M2s....so there are definitely plenty of 4GB sticks out there. I've heard that if your phone isn't designed for such a large stick, it generally runs a bit slower, but no problems. I've also heard that the older Sony PC software suites can't use cards larger than they're designed for because they crash when the program can't identify the size of the card. I think Mru5 is probably right about the firmware upgrade.