The new mobile payment system backed by three carriers (AT&T, Verizon and T-Mobile), dubbed as Isis Mobile Wallet, has been pushed back from its original September launch. A leaked internal memo, as attained by Tmonews (and as we’ve reported before,) shows that Isis will now be launched on October 22 in two cities – Salt Lake City, Utah and Austin, Texas. But the memo also reveals more details.

We now get a better glimpse of how the mobile payment solution works. In order to use Isis, you’ll have to apply for a special ISIS SIM card — regardless of the carrier of choice – that contains an NFC chip. This is probably done to improve the security aspect of the system, such as the remote wallet locking feature.

Especially for T-Mobile, the NFC-based payment system will work on the Galaxy S3, Galaxy S2 (software version LH2 or newer), and Galaxy Relay 4G (LH1 or newer) for now. As for Verizon, we know at least one device on the carrier that supports Isis, the Droid Incredible 4G LTE. For your information, the app, when it becomes available on Google Play, won’t work on rooted devices.

As part of the push to make Isis alluring for customers, users will get $10 when they activate Isis and an extra $15 when they “convert the Isis Cash Card to a reloadable prepaid card”. While only T-Mobile and Verizon have so far confirmed the bonus, we’re sure AT&T would offer something similar.

What good is yet another mobile payment system if you can’t use it in most places, right? You’ll be pleased to hear that you can use Isis Mobile Wallet at merchants that support Visa PayWave, MasterCard PayPass, Discover Zip, American Express, and Google Wallet.

As far as pilot project goes, launching the service in two cities is a not a terrible start. But the fact that it requires a special SIM card isn’t something that many customers will find too appealing.