My boss in my Americorps program was a Jennifer. She would always introduce herself as Jennifer and her voice mail said Jennifer--but with people she knew she was always Jen. 1 N. She always wanted to be Jenna--but so many people were used to calling her Jen that she couldn't get it to stick.
She moved to Atlanta last year to start a new job...and there were already 2 Jennifers. 1 Jennifer and 1 Jenn (2 Ns). She decided now was the time to use Jenna--so everyone in Atlanta calls her Jenna...but everyone who's known her before calls her Jen. We make fun of her for it ("Who's Jenna? I don't know a Jenna!") Drives her nuts...