It sound's like IVM is the perfect solution for your needs. It's main purpose is to act as an IVR system where people call in and select various menu options for information, bookings, order taking, voice mails, or to be transferred to a live person.
In terms of equipment, there are 3 different ways of connecting IVM up to a phone line:
A) Voice Modem
Advantages: Quite cheap (around $35)
Disadvantages: Audio quality varies and is generally ok, but not fantastic. Cannot transfer call to a live person on an internal extension.
Other: Uses existing phone line from your normal Telecom (e.g. at&t, bell, bt, telstra etc.)
Info: All you require is a TAPI compliant voice modem and you're ready to start taking calls. Simply install the modem on the computer running IVM, and connect it to an existing phone line. IVM should then be able to answer calls and detect user input for menus.
Telephony Board
Advantages: The more professional option, higher audio quality, can handle more than one phone line simultaneously, can transfer to live agent extensions
Disadvantages: High cost (upwards of $200)
Other: Uses existing phone line from your normal Telecom (e.g. at&t, bell, bt, telstra, etc.)
Info: Much like the Voice Modem option, once the board is installed and connected to a phone line it's ready for use with IVM.
C) VoIP
Advantages: Quite cheap (some services even offer free private incoming phone numbers and you don't pay a dime to use the service), Can handle several simultaneous calls at a time (depending on provider), Does not require purchase of additional equipment, or the purchase of phone lines from your existing Telecom
Disadvantages: Requires a high-speed Internet connection, and is not recommended for Satellite connections (like a satellite phone, there may be delays in transmission. If the line is solely being used for an automated menu IVR system, this delay may be acceptable and go by unnoticed). Audio quality can vary significantly based on conditions of the network/Internet connection or even your geographic location in relation to the provider.
Other: Generally works well for most users and organizations who have a high-speed connection and a basic understanding of computer networking
Info: Unlike the other methods, this one requires no purchase of additional hardware or equipment. IVM can connect directly to a VoIP service to answer phone calls. Many VoIP services offer very cheap rates in comparison to the major Telecoms and some even offer free incoming phone numbers.
Note that although Vonage is technically a VoIP service, it is atypical in comparison to others. Vonage locks their hardware so it can't be used with other equipment or software like IVM. In essence, Vonage can be treated as a normal analog line similar to the one you may have from your current Telecom provider. Thus in order to connect a Vonage line to IVM you would have to use either method A or B. P.S. Vonage is also one of the more expensive VoIP services (it is also the most well known).
