You can edit the ForceCellConnection string value under HKey_Local_Machine\Comm\InternetSharing\Settings to say "Sprint PCS," or delete it entirely to get back the option to switch between Sprint PCS and Phone as Modem within the Internet Sharing app. I'd just set it at Sprint PCS, that way you don't have to worry about it in the future. There is a cab floating around somewhere to import the reg entry for you, if you're not comfortable editing it yourself.
I've attached v.91 of WMWiFiRouter. This cab will also set up an adhoc WiFi network for you with the name "Free Viruses!!" (you can change the name, or set up your own peer-to-peer/adhoc network if you want, that is just the name I chose). Make sure your WiFi switch is in the on position before activating the program. Give it a try and let us know if you have any more questions
Edit: Sorry, give me just a second to upload the cab.