This should get you into engineering mode of the modem, In the Gemtek series you can set special frequencies. Give it a try.
1. Download an install your favorite Tamper Proxy. I used TamperIE for Internet Explorer. You can get it from »
www.bayden.com/tamperie/ Configure it to "tamper with HTTP Posts".
2. go to 192.15.1 and log into the device. the default password is either "motorola" or "CLEAR123"
3. Once in, go try to do something (like change the password), and hit "save"
4. when the TamperIE window comes up, click on the "PrettyPost" tab on the bottom.
5. In the left column, you should see something similar to "webui:settings/password". Chage that to "webui:settings/provider/ISPName" In the column to the right, type in "Clear" (You might have to make this "Clearwire" if "Clear" doesnt work. Now click "Send Altered Data"
6. now repeat steps 3-5, only this time change the password field in the left column to "webui:settings/enable_customization" and the value in the column to the right to "1". Now click "Send Altered Data"
7. if all goes well, when you load the page with the WiMax settings, it should let you edit the realm. You should now also be able to edit everything on the "telephony" page.
Good Luck! Let me know how it works