Force9 allow you to have more than one 'home' number, I think it is 5 so you can connect on a 20-hours-per-week (or whatever you end up paying for) from any of the 5 locations (I'm sure they will check to see that you are not connecting from more than one at a time) and then you can have a pay-as-you-go from anywhere else.
Their customer service leaves something to be desired but the service is good