You clearly believe in this but please could you explain how you see it working in the case of giffgaff where you can change goodybag each month and choose only to have a goodybag some months not others?
Let us take as an example someone who used 5 - 6 gb per month.
Currently they would purchase a £15 each month.
If they had roll over data could they purchase a £20 goodybag every 3 - 4 months, or a £20 in month 1 and a £5 goodybag in months 2,3 & 4.
That could be quite a hit in income for giffgaff.
And how is the £25 always on goodybag treated?
If you used £15gb in month 1 how much data should you be able to roll over given it has no specific limit? 5gb, 10gb, 15gb?
Where a 12 month contract, which does not have the giffgaff flexibility, is in place I can see the argument for roll over data.
In the case of the giffgaff model I cannot see how it would work fairly, but perhaps you could help me understand how you see it working.