Mobile Broadband is all about accessing internet on the go and all the time. WiFi is limited to only finding hotspots and at all other times you will not be able to access the internet. There are many other Wireless Internet options available like Wi-Max, satellite, etc but mobile broadband seems to be the best service nowadays for people constantly traveling across places.There ia a larger problem with satellite broadband it is broadband only in the Internet to home direction and not for the home to Internet direction, you still will need a physical connection, usually this where a mobile solution pitches in best. Most folks I know use Mobile broadband through your cell, but the cost is very un-prohibitive, and I am sure it is very expensive at all places around the world. However, you may encounter roaming charges too when you leave your base network in most places and this charges are just over the roof.
The most important decision if you're using the internet that much is to choose a mobile broadband deal that has a big enough data option - you need to make sure you don't go over your data limit or you could be hit with big charges from the mobile network and when I say BIG it is simply HUGE.
Let's say that you're planning to use it for 15-20 hours a week, and that's mainly web and email (and not much youtube / downloading) then I would say that you're going to need atleast around 3GB per month(on the MAX side). Consider getting a larger data plan is absolutely safe. Most mobile networks currently have great deals where they don't charge overage - atleast after the iPhone launches.
There's loads of good deals around at the moment - try http://www.broadbandexpert.com for a list of all the networks offers and do mail me if you still have queries - I can surely try to help you as usual.
