This is a somewhat known process to many HUKD members but I thought best to post to provide a full rundown so everyone can reap the benefits.
It does seem pretty long but I think it's worth it for 50% off any digital purchase on certain Stores.
Plus, reap the benefits from O2 Priority and O2 Rewards.
Click Get Deal to go to the O2 SIM order page, fill in your details and tick both boxes at the bottom. It'll usually take up to 3 working days for the SIM to get to you.
Put the SIM in your phone, boot up and call 4444 to top up £10.
Text FREE10 to 21500 and wait for the confirmation that the bonus credit has been applied. Takes up to 2 hours. Phone 4444 again to confirm this before moving on to the next step.
*** If you're using all the credit on Google Play the tutorial ends here, enjoy. If not, move on ***
Go to your SEN account online and select Add Funds to Wallet, Mobile Top Up, enter £15 and the O2 phone number. Reply Y to the text message to confirm, this message costs 10p out of your credit.
Youll be left with £4.90.
*** If you're on an iPhone the tutorial ends here. There's £15 for your PSN Wallet and £4.90 for airtime.
If you're on Android, carry on ***
Go to Google Play and spend at least £4.40, best advised you add whatever you're buying to your Google Play Wishlist to find them again quicker.
Find an app or game, click Buy and then the Google Play Balance, check Other Payment Methods and select O2 Billing. It'll verify and then put you through to the payment window. Make sure where it says payment method it shows as O2 Billing.
You should now have 50p or less in credit. Again, this can be confirmed by calling 4444 or texting Balance to 20202.
You're now eligible to use O2's Lend Us a Quid service.
Call 4444 and select option 6, hit 1 to confirm. This will add £1 credit lent by O2.
Go back to Google Play and refund the apps or games purchased. You'll now have £5.90 credit.
Go back to your SEN Account as before and top up the remaining £5, confirm with a reply to the text and voila.
You've also got the 80p left from all that spare, so you can freely spend this in Google Play or use the credit on texts, calls or data.
Couple this with the Days of Play Sale on the PlayStation Store at the moment and you can grab Horizon Zero Dawn or a 12 month PS+ subscription for just £15, or there's God of War III, Uncharted 4, The Last Guardian or Ratchet and Clank for £10 each.
(They're not that price on the Store but that is essentially what you're paying out of your own pocket for them)
Edit 1: Xbox Carrier Billing instructions. Unsure as to whether they will charge as the PlayStation service does. http://www.xbox.com/en-GB/promotions/buy-game-credit
Edit 2: Some purchases from PSN will require the above to be done more than once.
I'll look to edit this as questions or new methods come in.
I feel like I need to add this: P-L-E-A-S-E do not overuse this method. They used to offer 20 quid instead of 10, until too many people abused it by ordering too many in too short a time period. A few a month is grand.