Just signed up to virgins $20 byo phone plan which allows you to roll over unused credit and there is an additional bonus of 1gb per month!
200 dollars credit plus 1gb is a pretty good deal to me. Especially when it is 4g compatible. Great for those who got the nexus 5 and don't need a plan with a phone.
Shows how much they know at their call centres. There is no 4G specific sim..