George, you can use I-modems but they consume 2 B channels of a BRI and
only allow ONE 56k X2 channel per BRI. If you use a USR modem pool you can
get 8 BRIs and get 16 B channels out of the deal that you offer either
33.6, 56k, or ISDN on. Going rate of a MPi-16 is about $5800. You can plug
them into serial ports or a term server. You can also get a netserver 16 by
USR for about $7000.
These will give you easy 56, access without moving to a PRI solution.