Just a bump here - I have lap infant on award ticket US-Mexico. No extra mileage charge. However, I cannot change the ticket online - but instead need to call UA. Routine change in flight that should take all of 3 min online. This is a not-insignificant PITA given how phone service has deteriorated even for 1Ks. Any work-arounds? (Beyond adding a lap infant closer to departure, assuming it doesn't have additional cost.)