[Rally1]

Many of these questions are in their FAQ. I have yet to see anyone get hit for tethering on Sprint using ICS or USBmodem or similar.

KB0802011: Providers and detecting tethering

We often receive the question if providers can detect if the user is tethering.

WMWifiRouter does not do anything specifically that lets your provider know you are tethering, though in some cases, Internet Connection Sharing might.

Aside from that, if you are a heavy tetherer, your provider will always be able to detect this - it's the question if they actually do. If you tether once in a while to browse some simple webpages or check e-mail, chances are fairly small that this will raise any flags on the provider's end. However, if you are a heavy user who uses a lot of bandwidth or download through P2P programs like BitTorrent, the chances of their systems noticing something are a lot larger.

Though we have not heard back from any user that they have been charged for tethering, we always advise getting a data plan that allows this.