sometimes it helps to view this sort of thing the way that the system does.

Someone dials xxx-xxx-52xx (a number in your DID range).
The Telco sends you a DNIS number, such as 52xx.
The SX2000 says, "what do I do with this call?"
So it looks at DNs. There's a match for a speed dial, 52xx.
That speed dial points to extension 6xxx.
Call goes through, rings the phone at 6xxx.

Now, say that you have "absorb 1" instead of "absorb 0."
The telco sends 52xx, the SX2000 strips the 5, and looks at 2xx.
It says, "What do I do with this?"
So it looks at DNs.
There's a match for speed dial 2xx.
That speed dial points at ext. 6xxx.
Extension 6xxx rings.

This is what JohnP just said, but with a bit more detail.

Hope that helps.

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