Much of the episode is centered around Ted and Barney becoming a couple to raise a child together. Neil Patrick Harris and Josh Radnor actually played a couple in the play "The Paris Letter".
In the episode Marshall is trying to make a call. He runs into Ernie Hudson and asks him if he could borrow his phone. Ernie responds "Who you gonna call?" A play on him playing one of the members of the GhostBusters gang which had the theme song "If there's something strange in your neighborhood, who you gonna call? Ghostbusters!"