There seem to be very few suppliers at Corvera other than Telefonica(BT) or Telitec. Allegedly, Telitec allow you to pay only for certain months but at a higher monthly rate and pay for installation versus pay every month and free installation and lower monthly costs. This is the one I am exploring for next year.
The Vodaphone dongle which used to be 50 euro per month with unlumited use is now 20 euro per week!!!!!! extertionate!!!!!!
I have also tried Teleast who seem to have the most cost effective solution. However, they do not currently supply Corvera. It is worthwhile contacting them to express interest and gee them along to start supply to Corvera.