I was also porting my wife's line and I have an AT&T S4 for her, which worked fine so we switched out the sims to see if that would have worked but we had the same problem calling her number on my N5. When we called my number on her S4 it went through just fine.
I then put my sim back into the N5 after it was in the S4 and worked fully and then my N5 could make and receive calls. I vaguely remember people having issues on a brand new sim from AT&T with their N5 and commentators stating that if the sim wasn't activated on an LTE phone before the N5 that you would have problems.
Very strange but just wanted to give my $.02
And I am loving AT&T so far, very glad they dropped their mobile share plan prices for out of contract and were offering the $100 bill credit for each new line. Consistently getting between 10-20 mbps down in most areas and my wife is getting 40mbps down at her job, on Sprint my LTE was very spotty and only getting between 2-5mpbs with a rare jump to 10 or more.