From what I've seen (I have personally never done it, but know people that have), this is not typically enforced in any way, and you're probably fine entering completely fictional information for all of this stuff.

But...

I knew a guy in college (super disreputable, FWIW, so I don't necessarily believe everything he said) who claimed that one of the first tricks up his sleeve when he was launching a new site was to file complaints about incorrect WHOIS data against all his competitors (and sometimes against random sites with useful keyword content and a bit of pagerank) and then pounce on the domains if they opened up so he could point them to his new site. He told me that often enough to be useful to him, people either failed to respond to the verification requests in time, or had actually provided false data, and he was able to either snatch their domains or at least cause some trouble.

So I probably wouldn't recommend messing around with phony data, better just to set up some contact info that you don't mind having out in the open.