Strange behavior on one phone. All IP phones on SV9100.

One extension cannot call a handful of long distance numbers.
- Can call most numbers with no problem.
- Call a 'problem' number, get a reorder tone.
- Call a 'problem' number from another phone and it rings.
- Some of the 'problem' numbers are in the same building, same prefix.

I've tried moving the phone to different switch ports, swapped phones, all the regular stuff. I have found that if I change the extension number in the phone, it works! I cannot see any differences in programming between the bad extension number and a good extension number.

I would like to keep the original extension number and figure out why this is happening.
Thanks for any ideas.

Jim