Sprint is notifying their mobile hotspot customers the company is now prepared to enforce their formerly soft-capped 5GB plan with a $50/GB overlimit fee, billed at $0.05/MB increments.

Sprint has long informally capped customers using their phone as a Wi-Fi hotspot or tethered device, but until now was not prepared to enforce the limit because it could not accurately track usage.

“Starting June 2012, and effective on your next bill, your phone or tablet’s Mobile Hotspot on-network data allowance will be limited to 5 GB,” reads the message sent to Sprint customers.

Customers will begin receiving text message alerts when they reach 75% of their usage allowance, with repeated alerts at both 90 and 100%. When the 5GB limit is reached, Sprint will give customers the option of continuing service at the penalty price of $50/GB billed in megabyte increments, or shut the service down until the next billing cycle.

Some customers have been confused by the change, in part because Sprint has made a series of sometimes-confusing adjustments to their data pricing. But the company insists it has always had a limit on its mobile hotspot service, even if not enforced.

Smartphone customers using broadband on their phone still receive unlimited access. But other devices with mobile broadband access are usage capped based on the usage tier selected.

Other stories of interest:

1. Sprint Gets Customers Accustomed to Usage Caps: Mobile Hotspot Gets 5GB Limit Oct. 2
2. No Data Caps or Speed Throttles For Sprint Customers (Unless Roaming)
3. Sprint Paying Customers Up to $125 To Dump AT&T, Verizon, or T-Mobile
4. Verizon Wireless Hotspot Pricing Will Burn a Hole in Your Wallet With $20/GB Overlimit Fee
5. Virgin Mobile Introducing Unlimited Mobile Wireless Broadband $40 A Month on Sprint Network