Isis, the mobile electronic-payment system that is being tested in Salt Lake City, is extending the length of a promotion to entice more users.

Isis customers can now ride Utah Transit Authority buses and trains for free through March 31. The promotion originally ended Jan. 31.

Isis (pronounced eye-sis) can be used with certain Android smartphones (and in the future, iPhones) that have a special SIMM card installed. After an app also is installed, users can purchase goods and services at many retailers by just tapping their phone on a special mobile-wallet electronic reader.

It is free to register for Isis, through Verizon, T-Mobile and AT&T retailers.

Participating stores using Isis electronic readers include Foot Locker, McDonald's and Megaplex Theatres.

Customers can either set up their account to draw money from a charge card (at this point only American Express or a Visa from Chase or Capital One can be used) or they can feed money into a pre-paid Isis account.