The FXO numbers are Cisco item numbers. Of the ATA186 are only two versions out there. One has a higher impendancy for overseas power networks, but I assume this wouldn’t make really a difference since I am using the US version in Switzerland (you may consider it Europe, although not politically 😉 Whatever you buy will be fine. The Firmware should read greater than 2.2 but this can also be upgraded when you purchase one with a Cisco license. The licensing is a headache. The Vonage/Amazon version is not shipping with a license for instance, since Vonage has a license leased for the time you are a customer. For us normalo consumers a firmware release means a bugfix and should therefore be free, not so for Cisco. Cisco ships a router and you can not use it even without buying a software license for each and every functinoality used. It’s like buying a car and paying for every seat and and every light you want to see blinking in the control panel. Funny isn’t it?