Sorry, I missed your post earlier because my dealer training was when it was known as the SRX.
7 [R] is used to replace an instrument. 3 [E] followed by 10 digits is used for entering a new [E] extension.
If the phones blinked when you plugged them in, you should have used the digit 3. Now, they are recognized and can only be removed from the system by plugging in another phone and dialing 7 to replace it.

However, when you add a new extension by dialing 3 followed by 10 zeros, they default to factory settings which are never very useful (in my opinion). SRX was a very powerful system but required a 2 week training class to become certified.

- Dave S. -

You can never appease your ideologue opponents.