Dell U2713HM LCD Monitor Killing Wifi (and ethernet) on my Mid-2012 MBP and iPhone 4S
I want to post a quick update as I have been able to isolate the problem.

My MBP's magsafe power adapter was hooked-up to the same power strip into which my Dell display was plugged into.

Plugging the magsafe into a "discrete" power outlet solved the wifi blackout issue.

I hope this helps others dealing with similar issues...