Hi, I'm looking to update my lad's phone and want to use his existing ASDA pay as you go SIM. The handset he wants is £70 from ASDA but only half the price from O2 or Vodaphone shops. If I buy the handset from these networks will the handset be locked?, if locked for how long? or can I just put the Asda SIM in and away he goes? All help gratefully received Cheers!