wireless internet equipment questions

[prov811]

We're a couple of unlucky saps who can't get DSL or cable. A local company is offering wireless (LOS d/l; phoneline u/l). The rep mentioned we need an external dial back modem that plugs into their modem. What is he talking about and will a regular external modem suffice? Any other concerns about wireless we should know about? How about latency, other gaming issues? Thanks