I asked for the wheelchaire service for my mom when she came here in
February. All the major US airlines have this service. My mom flew on UA
for her trip. And at Chiccago O'Hare, someone picked her up at the arrival
terminal, then helped her go through immigration/customs, and then took her
to the terminal for the next flight.
By the way, I called UA about 3 days before my mom's flight.