Usually, these phoneshave an LCD display screen that will show you the caller ID on inbound calls. You can control multiple calls using a separate button for each call. Forexample, if you get multiple calls, each caller's number will be displayed. Youthen can either put the first call on hold and answer the second call or thesecond call will be transferred to voice mail. Conference calling is alsosupported by these telephones.
Prices range from several hundred dollars pertelephone and higher, depending on the features.
By the way, if you purchase anISDN telephone with an integrated NT1 interface, you can only put one telephoneon the circuit. You can now transportvoice and data simultaneously over your single ISDN circuit. So, if you are ona voice call and need to transfer a data file, send a fax or access the Internetat the same time, you have that capability. There are manydifferent brands available with many different functions. Some have an RS-232interface for a computer link and some come with an ethernet port for a LANconnection.