Roethe - I would suggest your actions will obviously speak louder than any words.
So, whatever you tell him from now on, perhaps back it up with proof. "Yes, that was my mum on the phone" .. then show him your cell phone with her number on it ... kind of thing. It's just an idea. But perhpas if you can encourage him (if that's even possible) to begin to believe you again, then that is a start. You have a long road ahead of you b/c he may doubt anything you tell him from now on. That is a heavy burden to bear.
Have you apologized to him? That you are truly sorry and told him the truth about why you lied? (that you wanted to impress him, etc) That it was perhaps your insecurities which inspired the lie?
It sounds trite, but have you asked him for his forgiveness? If he says "yes", he forgives you then you could BOTH agree to start with a clean slate.
And never, ever tell him lies again. The truth might be harder in the short term, but in the long term, it's beneficial to all concerned in my opinion. The other prob with lies is that you have to keep remembering them. I'm just lazy. The truth is easier.
That's my 2 cents worth

I hope it gives you some ideas.
Finally - I agree with the others. There is not really enough information to go on - what did you lie about?
Good luck and keep us posted.
- jazzie