[Skunkworks] Multi-port Voice-capable GSM modems

Hi, I am looking for some kind of interface/device that supports multiple GSM lines (and supports voice calls not just SMS) such that if I connect it to my machine I can have multiple phone lines to a PBX (asterisk in this case). Am told there might be some PCI-based cards that can do this. Are there any USB types? Anyone with any info (and/or quotes) for both PCI and/or USB types. -Billy