Trying to do the same. Some info i found.
From KydDynoMyte on slickdeals
"You don't have to wait until you remove Muve, but Sandisk did something special to these cards. You can't see the hidden 3GB partition. The only reported method I haven't been able to try yet (all the others have failed) is:
one guy reported doing this to 3 or 4 Muve cards. He put the sdcard in his Epson wireless network printer card reader and transfered over 3GB to the card and it let him do it, then he was able to reclaim the missing space. Not sure if once you get over 1GB on it if you get the whole missing 3GB back or only the space you write to. Also I hope he didn't have the older bad batch Sandisk sent out that didn't have a blue background and required the AAA SD Card fix on market for Muve to work."
SANDISK SECURE FLASH MEMORY TECHNOLOGY TO POWER NEW CRICKET UNLIMITED “MUVE MUSIC” WIRELESS SERVICE
"With the help of SanDisk, we have created an innovative new way to protect digital content without the use of DRM," said Jeff Toig, vice president and general manager, voice and data products, Cricket. "This solution enables a superior overall experience for Muve Music customers. They will have immediate and easy access to all the music they love while the music industry has the confidence it needs in a secure mobile music solution."