asterisk users - Nov 2006 - OT: Reflash Mitel 5220 from MiNet to SIP

Have some 5220's that are MiNet only and I was wondering if anyone has ever
reflashed it to MiNet/SIP. Tried to fake out the phone by redirecting it to
a TFTP server with the SIP image, it loads it, freaks out, and reboots. tia