So i'm off to the UK/Europe for 2 - 3 months in Europe and i'm going to need some mobile broadband.

Have used T-Mobile in the UK before and found the service to be far slower than NZ's mobile broadband, but after some research i found they were known to be slower than other carriers and O2 was the best for speed.

I'm going to be using 5-10GB.

Is their a carrier who is across all/most of Europe as i certainly don't want to be paying for those amounts while roaming.

If their isn't i have no problem with buying a local sim in each country but i don't want to buy a new dongle in each country - can you just swap sims in a dongle and everything will work or are they locked down to the carrier?

 Cheers