is there a way to keep withheld and blocked number calls from coming through on my iPhone?

As far as I know, there is no way to block those calls, but you should make sure your number is on the national “do not call” registry.

Also, you can put the phone in silent (vibrate) mode and the alarm will still play. This is what I do every night when I go to bed, and it always wakes me up in the morning.

i’m not sure if this is worth it, but this would definitely block unwanted calls

http://lifehacker.com/360480/get-your-grandcentral-number-today

the do not call thing is a good suggestion, but the blocked numbers I’m getting are stupid Kids trying to do a prank phone call and I have a feeling they don’t consult that list before they call

In that case, I’d get a new phone number and be very choosy who I give it out to.