[supadoggie]

If you have another sprint phone, you can just do a swap online. After you've done the swap online (and then the swap back), it will give you instructions for setup on your phone. You'll get some info and two codes:

Secondary 6-digit code: xxxxxx
One-time 6-digit code: xxxxxx

The secondary 6 digit code is the MSL number.

if you type ##MSL# into your phone, it will allow you to change the MDN and MSID numbers