Generally:
DID are for digital lines such as PRI, T1, and SIP trunks
DIT are for analog lines (POTS)
Analog DID trunks were more common in the past. They are usually digital now days. I have not seen analog DID trunks for quite some time, but as my username implies, I haven't been working with telephone systems as long as other people on this board.
Want a longer explanation of DID:
https://en.wikipedia.org/wiki/Direct_inward_dialShort version: With DID the PBX is expecting additional information about the dialed number from the phone company. Usually telco sends the last 3 or 4 digits (up to 7 for Toshiba) of the number dialed by the caller. Standard analog POTS lines only send caller's caller ID info, not info about the number they dialed. A single circuit with DIDs can have many phone numbers. I have seen several hundered phone numbers connected to a single PRI circuit. A PRI has 23 audio paths.
DIT just means that when the phone line rings, sent the call somewhere.
Basically unless you plan to change your phone service to something that supports DID, you will be setting DIT for your analog lines. If you want DID with a small number of lines, I would ask your service provider and your Toshiba dealer if they both support SIP trunks.
A couple of advantages of DID is that you can give everyone in your office a direct phone number (or specific people that can use a direct number), you can have a 'back door' number to access voicemail, you can have multiple company greetings with different phone numbers, you can have numbers for various departments, like billing, shipping, etc.
But this is not something you will be changing. Only your Toshiba dealer and your telco provider will set this up.
