Cordless phone I have a Norstar 3 x 8 system, with one m7310 and 3 M7208 phones and would like to add a cordless phone to system. Which one do I need

Before you can do anything you need a M7310. Programming a Nortel voice mail requires M7310. It uses the 3 soft keys under the display to program it. You can get one cheap on EBAY. Next you need to find out what type of Voice Mail System in connected to your Nortel phone system. Below is a link to a Older StarTalk manual. You may have a StarTalk, StarTalk Flash, or a Call Pilot.
http://www.myuserguides.com/Nortel_Norstar_Startalk.pdf#page=15&zoom=auto,-69,407

Below is a link that tells how to reset the System Manager Password.
Reset Admin Password Norstar Meridian and Nortel BCM Help Guides

The default code and password for System Admin is F983 and 1020000 or 1021111. The photo below shows a system admin programming tree. Hope this helps
Charlie

Nothing in programming typically would help with exception to maybe swap by plugging in a M7208 into your problem jack then swap back to m7310 again. Going to 08 and back to 10 can sometime clears issues otherwise sounds like a bad phone and needs repair.

nope not possible

Dial "F * 0" (Feature, star, zero), which is Button Inquiry, and press an intercom button to see the extension number of the telephone. If Set Relocation is set to "Yes", then the extension number & mailbox will follow the phone when it is moved. Move only two phones at a time, and wait until they completely "boot-up" before moving additional phones.
Hope this helps.

Feature 805 is valid on versions 2.0 or above.

It could be a simple as the phone has call forwarding to another extension set up on it or the direct line could also be programmed on the other set. Does the screen on the non- ringing m7208 display "forward to:xxx" or does it display the current day and time?

Changing the time on a Norstar system must be done using a display phone. Using a M7310 or T7316 the right 2 buttons under the display are "NEXT" and "SHOW" respectively.

1.- To enter programming mode press "FEATURE" and "* * 2 6 6 3 4 4" 2.- Enter password (default = 266344) - display should read "Terminals & Sets" 3.- Press "NEXT" 5 times - display should read "Time and Date" 4.- Press "SHOW" - display should read "Hour:___" 5.- Press softkey "CHANGE" 6.- Enter hour - display should read "AM OK or Change" 7.- Select AM or PM 8.- Press "NEXT" - display should read "Minutes:___" 9.- Press softkey "CHANGE" 10.- Enter minutes 11.- Press "NEXT" - display should read "Year:___" 12.- Press softkey "CHANGE" 13.- Enter year 14.- Press "NEXT" - display should read "Month:___" 15.- Press softkey "CHANGE" 16.- Enter month 17.- Press "NEXT" - display should read "Day:___" 18.- Press softkey "CHANGE" 19.- Enter day 20.- Press "NEXT"

If the extension was a swap of the old M7310 with a new(ish) M7310 no additional programming should be necessary. However if the phone was replaced with another type of nortel set(M7208, M7324,T7313 etc.) then the phone will default to its base features. To re-program the feature keys press feature *3, the button you wish to program, and the feature code for that button

Increase the contrast of display of ur phone it might fix the problem

I need more information. When calls come in, does the triangles appear on the phones you want to pick up? Do you have all the lines on the phones? Is sounds like you want only the "ringing sound" to happen on your phone, but have it appear on the others. Is this correct??