Free O2 Text Credit To get 300 free texts on a new O2 sim put it in your phone, switch on and wait for the welcome to O2 message. Then text (free) the word BALANCE to 20202. You'll get a confirmation text and the freebies take immediate effect. To get an extra Â£2.50 you can register the sim with O2 by sending you Name, House Number, Postcode by text to 21500 - this is applied after 2 days. You need to be an existing O2 payg user ,and have a spare brand new free sim.