Modem banks are simply that. A bank of modems just like you use on your home PC that require each modem in the "bank" to have a separate telephone line for each and every modem. This is basically old technology. A lot of small, independent ISP's used this method to allow their users to connect to their gateway to the internet. These are analog circuits and have been pushed asside for their limitations and replaced with digital hardware. I have set up 2 small ISP's that use hardware developed by Lucent Technologies. ( click here for reference )
These products are basically an ISP in a box and connect to digital phone circuits ( DCS circuits provided by your TelCo ) for the incoming users or both if used for VPN or VOIP, and your gateway router to the "Cloud"

I hope this may offer some insite, as for your original question, what specific use do you have a need for a terminal server? A bit more information on your project would be helpful for us to give you a less general, more detailed answer.