its only £1.50 why not pay for it and find out?
Anyway we used to do it years ago basically you have 2 fones of the same network call the topup line on both, holding 1 phone in each hand, when it asks you to enter the topup number enter the number on both phones at EXCACTLY the same time.
We done it with 5 chipped C12's, we wanted lots of credit on each phone so that you wouldn't have to keep rebooting + redialling when the tenner ran out whilst phoning abroad.
Basically we bought 5 x £10 credit vouchers, gaffer taped the phones to a table, got a peice of wood and hammered nails into it at excactly the distance between 2 phones(ie the distance between number 1 on the first phone and number 1 on the second phoene etc) and at the same depth.
now we had a stick woith 5 nails in it we placed the stick above the phones and dialled the topup number and then entered the voucher number using the stick, each time you pressed one key in all 5 would be entered at the same time. All in all we put £50 on each phone for £50.
people were using the double top ups on all the networks but they got wise to it and started cutting the phones off.
woth a try with some free 02 sims though!
i'd be interested to here if anyone actually tries this and succeeds