Sprint CEO Dan Hesse has said the company will stop offering unlimited plans if they become unprofitable, and apparently that time has come – but only for some of its devices.

Sprint told its customers yesterday that it would stop offering unlimited WiMAX service for tablets, laptops, USB modems and mobile hotspots. The change does not affect smartphone customers on unlimited plans.

“Effective beginning with your next bill following notification, your on-network monthly data allowance will no longer include unlimited 4G,” the company said in a post on its support page. “If your phone plan contains unlimited data, you will continue to enjoy unlimited data usage on your phone while on the Sprint network.”

Customers with 3GB of 3G data and unlimited WiMAX access will now be subject to a 3 GB cap for data use on both networks, with an additional charge of 5 cents per megabyte over the cap. The same applies for customers on plans with 5 GB caps and 10 GB caps on 3G data – the limit now applies to data usage on both Sprint’s CDMA and WiMAX networks.

Customers who pay an extra $30 per month for Sprint’s mobile hotspot plan will be capped at 5 GB for data accessed through the feature, with an overage charge of 5 cents per megabyte.

A Sprint spokesman could not be immediately reached for comment on the changes.

Some analysts have predicted the impact of the data-hungry iPhone could force Sprint to abandon its unlimited plans to protect its bottom line. Speaking of the plans, Hesse recently told Wireless Week, “If something is not profitable, we won’t do it.”

Still, Sprint hasn’t given up on its all-you-can-eat smartphone plans just yet. The service is an important differentiator from competitors AT&T and Verizon Wireless, neither of whom currently offer unlimited data.