How can I unlock a Motorola ic502 to be able to use it for Direct Talk only?

[Frank]

I recently acquired a used ic502 that was previously set up on the Sprint network. I understand that this is a combo CDMA/iDEN phone, so I'm confused on how to go about setting it up so that I can use it strictly for it's off-network Direct Talk capability. The phone no longer has the original Nextel SIM in it that it was paired to, and all I have access to is a Boost mobile SIM that results in a "insert correct SIM SIM card does not match stored account information" error message. I can't do anything except make a 911 call with it like this. I also tried without a SIM, and again, all keys are useless except 911 and vol. control. I know it needs a SIM in it to work, so I'm assuming that I will need to unlock the phone so it will accept the Boost SIM so that I can navigate around on it and put it in Direct Talk mode. My question then is this: Is unlocking via keypad possible even without proper "paired" SIM? and secondly, if not, is there any way to Unlock / Flash this phone using the USB cable and PC (Preferred method)? Where can I find the proper software and instructions on use (preferably as cheap as possible, free is always good)? My plan is just to be able to use a Boost SIM as a sort of "Dummy SIM" just to allow the phone to be used for it's off-network Direct Talk 2-way capabilities, I have no desire at all to use it on ANY network, just for 2-way....any suggestions? Thanks!