This was a support question, not a general comment.
For PSTN, the details depend on the country. In Germany, I believe that DID digits are in addition to the normal number, but, in most countries, a block of normal numbers is used, so that the number length remains the same. This can sometimes cause problems when calling Germany from abroad.
Excess dgits on non-DID lines need to be handled by something like Read or DISA, and there will need to be a pause, to ensure the call is answered.
Note, in this thread, “DID” is used in its traditional sense. “DID” as used in the Asterisk work is only really DID on the incoming side of the service provider, and may well be pooled with other customers.