OK, with a wireless ISP, he'll have an antenna/receiver outside, and a station inside, most likely running Power over Ethernet to the outside. The station inside will have at least one ethernet port, and probably a full router/switch, and possibly a wireless LAN (802.11) as well.
As far as what he needs to get, consider the station inside to be just as if it were a cable modem from a regular ISP. The ISP will be able to tell him whether the station has a wireless LAN as part of the equipment or not (it likely does, nowadays). If so, then he won't need another router/gateway unless he wants more speed/features than provided by the built in wireless.
Mike