PSTN to USB phones

Hi guys,
Can i ve a configuration with motherboard having 12 USBs(i.e 12 extension ports) & 1 FXO card(4 ports).Does asterisk support the USB phones.If so Please guide me to go ahead.

I mean using ethernet interface of the PC-PBX & connecting to a kind of switch which has RJ-11 ports.1 RJ45 to 12 RJ11 ports