In yet another move highly suggestive of a major product announcement pending at Sprint (gee, what could it be), insider sources at the company have told Sprintfeed that Sprint plans to cap its tethering plans to 5 GB of data per month starting October 2. Mobile data that goes straight to the phone will still be unlimited (or as "unlimited" as such plans ever are), which remains a key advantage that Sprint will hold over rivals AT&T and Verizon should the iPhone actually launch on its network next month.
Like AT&T and Verizon, Sprint charges an additional monthly fee to tether mobile phone data connections to another device, such as a laptop or iPad. In Sprint's case this fee will end up being US$29.99 per month for 5 GB of data, which contrasts with $20 per month for an additional 2 GB from Verizon or AT&T. There's obviously no indication yet whether or not this pricing will apply to the (still theoretical) Sprint iPhone, but it seems likely.
So far Sprint has raised its Early Termination Fees, discontinued its Premier service, raised its upgrade fees, and has now capped its tethering plans. These are all quite consumer-hostile moves on the carrier's part in the lead-up to a supposed iPhone launch, and they don't paint a particularly rosy picture of the company's stance toward its customers. Despite rumors pointing to Sprint offering the iPhone with unlimited data in the relatively near future, it's worth noting that other networks who shall remain nameless have buckled under the strain of "unlimited" iPhone data in the past and have summarily discontinued those plans.