may be TDM2400 for enterprise and TDM400 for SOHO ?
That sounds right. The big difference is that the TDM2400 is a big card that has 24 spots for FXO or FXS modules while the TDM400 only has 4. So, if you have a lot of connections that need to come in (from non-voip phones or from POTS), the TDM2400 is a sweet deal because it only takes one PCI on the motherboard.
The other difference is that the TDM2400 appears to connect with the wires (ie a punchdown block) rather than with the typical plastic heads. So, you have to wire it directly in to the card (how the heck would you fit 24 jacks on the end of that card!?!)