Isis on Thursday became available to smartphone owners nationwide. The new mobile payment service allows people to make payments at select retailers around the country by tapping their phones on the Isis terminal at check-out. Support for the venture is somewhat limited, however, and users will have to make an effort to sign up.

For starters, Isis is only available to AT&T, T-Mobile, and Verizon Wireless customers. These three network operators backed Isis from the start. Sprint is not a part of Isis, so Sprint customers have to stick with Google Wallet or other mobile payment services. Second, the system is limited to those who use American Express and Chase credit cards. Those with credit/banking cards issued by other banks won't be able to participate. Last, the service is only available to Android smartphones for now and requires users to buy a new, secure SIM card, and download and install the Isis app on their phones.

Not all phones are supported, but the list of compatible devices at AT&T, T-Mobile, and Verizon Wireless is pretty good. For example, about a dozen phones sold by AT&T -- including the HTC One, Samsung Galaxy Note 3, Note II, S4, S III, and other handsets -- are already good to go. On T-Mobile, the list includes all these same devices. At Verizon, phones such as the LG G2, Motorola Moto X, Droid Maxx, Droid Mini, and Droid Ultra all make the cut. Each carrier has its own version of the Isis mobile application.

The iPhone is not yet supported. The iPhone doesn't include NFC. Isis is preparing a separate sleeve for the iPhone that includes an NFC radio that will talk to the handset. Isis hasn't said when the sleeve will be available, nor how much it might cost.

If you meet all these criteria (carrier, bank, handset), then you're welcome to sign up for Isis and start making mobile payments.

Where can you buy goods by tapping your phone? Plenty of places. A quick search in midtown Manhattan revealed dozens of vendors that accept Isis, including Duane Reade, RadioShack, Walgreens, Toys'r'Us, Rite Aid, Foot Locker, American Eagle, Footlocker, Champs, Jamba Juice, and of course the local AT&T, T-Mobile, and Verizon Wireless shops. The list even includes local businesses, such as the Westway Diner, StarLite Deli, and Brother's Famous Deli.

The system uses the near-field communication radio that's included in most modern smartphones. The NFC radio links the handset to the account and the associated credit card. Isis users need to enter a PIN code each time they make a purchase, and the service can be remotely disabled in the event of a lost or stolen device. Everything is encrypted for protection. A unique transaction ID is sent with each payment transaction, making counterfeit use of the owner's card more difficult. Sensitive payment information is stored on a special chip in your phone called the Secure Element, which is designed to allow access only to authorized programs such as the Isis Mobile Wallet.

The future of mobile payments is finally here, at least for some people.