my phone# shows up as "private number" for out of state call

[cjchang]

When I call my parents in Ohio (landline) they see "private number" on their callerid instead of the phone number and/or name. As a result they ignore the call . When calling from our sonic phone# to our cell phones (same area code) everything works as expected. I see the sonic phone# appear on our cell phones.
Is the out of state behavior a problem on the sonic side or my parents' side? When I call their landline from our cell phone our cell phone# pops up in their callerid, as expected.

[dane]

I would expect this is some issue with their carrier, as we have never heard a report like this from anyone else.

[srpapas]

This happens when I call my in-laws too. I haven't asked anyone else if they are seeing the number blocked.