A couple of access numbers

The number from poketalk is 07924-000-108

Discussed on MoneySavingExpert here.

I haven’t tried it myself so no idea of whether you will be charged and what the quality of the line is.

 

Another service is from Call Discount:  020 3347 3399

This should be inclusive from a landline or mobile. Expect variable quality of line as the margin on this service is very small.