The concept of Duo is simple -- you have one Globe SIM with two numbers associated to it: the usual mobile number, plus a landline number. When you place outgoing calls to a landline, it automatically selects your landline number so that it becomes an unmetered, local landline-to-landlne call. When you call a mobile number, it automatically selects your mobile number as the call originator so that its treated as a mobile-to-mobile call. And people can call your phone whether they dial your mobile number or your landline number.
Globe charges postpaid subscribers P399 per 30 days for the service. There is a minimum lock-in period of 3 months from the time the service is activated. After that, you are free to deactivate it anytime.
P399 per month is actually not cheap. In comparison, I'm only paying P250 per month for my PLDT wireless landline. But the reason why I prefer Duo is because it does not require a separate phone. As it is, I already have 2 mobile phones -- 1 Globe and 1 Smart. Adding a 3rd phone for a PLDT landline is a bit too inconvenient already. Besides, I availed of a P250 per month discount with Globe for the next 24 months as part of their retention program. So the net addition to my subscription is only P149.
As a little bonus, I received a pretty good number as my landline number -- 9xx-1111. It almost looks like a vanity number, but its not. I just got it by pure randomness. I did not pay any extra to get assigned that number.