If you are using T-Mobile hotspot and would like to use the Guest OS also to get access to the net, do the following:
- Use host only networking with DHCP on the guest OS (Windows XP, in my case).
- On the native OS (OS X), configure internet sharing of airport with en2 (this is the Parallels Host-Guest Adapter). You would now see that the connectivity on XP goes out and then is re-established. Now, XP would have connectivity to the net.