Just an addon to number 2.
If your our of credit (over the month etc) then you can still access your account at Three website to allow you to topup.
Right now when you say voucher is this a special type of voucher or just the same as a 3 voucher you would buy over the counter at a supermarket or petrol station. Though this is what i was wondering how do you activate that voucher onto the mifi device as it hasnt got any buttons or that (is it via the website)
Also about the whole activating when topping up im still a bit confused if i were to top up on the 15th of the month would it last till the 31st or to the 14/15th of the next month. (Whilst the sim is in the mifi device)