Depending on the mobile phone's carrier, tethering may be provided at no extra cost. However, some carriers impose a one time charge to enable tethering, while others forbid tethering or impose added data charges, examples include T-Mobile in the UK. Often phone contracts that advertise unlimited or "all you can eat" Internet and data usage will bury these hidden charges in their terms of use.

As cited in Sprint Nextel's Terms of Service, "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."[4]

T-Mobile USA has a similar clause in its Terms & Conditions: "Unless explicitly permitted by your Data Plan, other uses, including for example, using your Device as a modem or tethering your Device to a personal computer or other hardware, are not permitted." [5]

Verizon Wireless and AT&T Mobility currently offer wired tethering to their plans for a fee, while Sprint Nextel offers a Wi-Fi connected "mobile hotspot" tethering feature at an added charge.

Not sayin' I agree with this. You pay to get data, why do they care where it goes? Why does texting cost so much?