The Turbo SIM I ordered from ebay works - I've got the phone using an Orange SIM now.
Needs a small hole cut in your SIM card to work with the chip on the Turbo SIM.
You need to slide the Turbo SIM in first under the SIM clip (it reverses under the clip as the chip is too big to slide under the clip) then slide the SIM card into place.
Standard Turbo SIM code works with the X8
Cost is £4.80, ebay item number is 290528060336