Sprint, the last remaining major national wireless carrier without an Internet Overcharging scheme, will adopt one of its own on Oct. 2 when it begins limiting 3G/4G Mobile Hotspot customers to just 5GB of usage per month with a huge $50/GB overlimit fee (charged in megabyte increments).

SprintFeed shared the details in a copy of a leaked internal company newsletter announcing the changes:

(click to enlarge - Courtesy: SprintFeed)

It is important to note Sprint currently plans no usage limits on their tablet or smartphone customers — this usage cap only applies to customers signed up for the Mobile Hotspot option who use their phone’s Wi-Fi feature to connect other wireless devices.  Those with third-party tethering apps or other “unofficial” tethering schemes won’t face the usage cap either, so long as Sprint does not initiate a crackdown on customers without a company-sanctioned tethering plan.

Customers will automatically be “migrated” to the new $29.99 usage-limited Mobile Hotspot plan in October.  Affected customers will be notified of the changes in bill messages or postcards.  Sprint will not grandfather existing customers.

Some Sprint customers claim the company has always had a “secret 5GB cap” on the Mobile Hotspot feature, only enforced when customers considerably exceeded it, but this makes it official.

Sprint may be preparing its network for the introduction of iPhone 5, which Sprint is rumored to introduce early next month.