InternetSharing WM 6.0:
Go to [HKEY_LOCAL_MACHINE\Comm\InternetSharing]
Then Delete "Extension"="rilphone.dll"
then change "MaxCMCon.... from 1 to 0..
MaxCMCon might be 0 already if so its cool.
InternetSharing WM 6.1:
Go to [HKEY_LOCAL_MACHINE\Comm\InternetSharing]
Then Delete "Extension"="rilphone.dll"
After that edit the dial "Phone as Modem" to "Sprint PCS"
MaxCMCon will already be 0.
I tether with just unlimited data plan and have not had issues. I wouldn't recommend downloading torrents (GiGs of data) as I feel it would eventually ruin it for all with the "Free" tethering. I know you didn't ask but here are a few more I use with every Rom.
Undock Keyboard
HKEY_CURRENT_USER\ControlPanel\Sip\Now
go to DragStyle and change (0) to (1)
A-GPS reg edit
HKLM/Software/HTC/SUPLAGPS/
GPSMode --> Change to 4 (orginal value 2)
faster web browseing..
HKLM\Comm\Tcpip\Parms and changed the TimerWheelSize to Value of 5 from 11
Rev-a
Dial ##778#, choose edit, enter your MSL, go to Data Parameters, Choose Rev. A, Choose Enable/Disable jury is still out on this one but there is a Rev-A thread already so look
HERE for your own conclusion.