Will I have to pay VAT on an iphone sent to the UK?

I bought an iphone 4 (non contract and unlocked by ATT) here (in the US) and i'm sending it as a gift for my girlfriend. I want to send it to her, but I don't know if I will end up paying customs or not? Is there a price limit that I have to be under to not pay VAT?

Thank you

Added (1). I'm guessing there's no way to avoid it, unless I do not declare it right?

Na you gonna have custom charges, if your on holiday just take it with you, or face the charges

She will pay import duty.