I have a Galaxy Nexus on Mobilicity. The gnex is a pentaband world phone but Mobilicity doesn't roam outside the US and Canada.
My wife is on the iPhone 4 with Rogers. I'm pretty sure she would be ok but I won't be.
Still very preliminary with the planning but tentatively one of us would use BA which has a connection in London as far as I know.
Aeroplan would likely be a connection through Narita.
The message drop sounds like a winner but when traveling through Europe, I have problems with 800 numbers and have never travelled to Asia. Not sure it calling cards purchased in NA would work from Asian payphones (ie is an 800 a toll free number in Asia?)
Gnex is unlocked. iPhone is locked to Rogers