Congratulations on your new baby. My son, Ian (who is now 8 months) old was born with hyperphe also. At first I was so scared and like you, shocked that I had never heard of PKU. It was a very hard thing to hear that something was wrong with my baby.
He is doing very well though, when he was born his level was 5.6 and it had been around 3 until he started eating more foods. Its really a trial and error to see what food they can tolerate when they have mild PKU. Of course, right now Ian is on the everything but meat diet, but his levels have raised quite a bit from bread and pasta.
I have to agree with AceMommy, once it settles on you and the shock wears off you will be so thankful that your son has such a manageable condition, compared to some of the other terrible things he could have.