Not a glitch as such, but it would seem ANYONE can take advantage of the 'Existing Customer' offer from Three. Some decent deals to be had here, noteably the S7 and Edge deals.
Have just got myself an S7 edge for £41 per month, £0 upfront. with 300 min, unlimited text and 12gb data. Topcashback also tracking at £99 cashback, and a £50 amazon voucher. Works out at £36.83 pm after cashback in effect.
All you need is ANY existing 3 Mobile number to take advantage of this. Whether this be a friend/family/pet/whatever else - just has to be an active PAYG or Pay Monthly Three number it would seem.
S7 from £30 pm
S7 Edge from £34 pm
iPhone 6S from £30
LG G5 from £25
Three might not be everyone's cup of tea, but I had been searching for a decent package with the S7 Edge and happened to come across this which seemed to beat anything else out there at the time.
Don't forget topcashback ;)
Amazon voucher is redeemable after first bill has been paid.