Using dial-out modems with voip

[dualarrow]

Hi,

I've been looking around the net trying to find info on setting up asterisk so it can work with a modem. Not using the modem to connect to providers, but for support calls to clients. So Astersik would have an FXS with a data modem connected that would be used to connect to client data modems for remote control of their machines for support.

My question is what codecs would allow this to work, and what speed limitations would be likely.

Thanks,
Andrew