The carriers do not like hotspots regardless of the os.
"There are, however, plenty of other features that can be used only if the network operators let you. The most desirable, enabling the phone as a Wi-Fi hotspot for up to five users, is likely to come at a hefty fee from many providers."
I seem to recall that relatively recently the US carriers started to threaten customers who did this with various penalties if they did not buy a plan that included a fee for this facility. Currently I believe that Verizon, AT&T, Sprint and T-Mobile all charge for tethering in one way or the other and customers risk punishment if they tether without permission.
From Sprints terms and conditions:
"Except with Phone-as-Modem plans, you may not use a phone (including a Bluetooth phone) as a modem in connection with a computer, PDA, or similar device. We reserve the right to deny or terminate service without notice for any misuse or any use that adversely affects network performance."
This has nothing to do with whether you run iOS, Android or WP7, the carriers are just being their usual selves - nothing to do with Redmond, Cupertino or Mountain View on this occasion.