I haven't worked much with phone appends since my previous position, where we needed it for a calling program. So perhaps things are better now, but we also had concerns about the quality of the data.
Our basic rubric was that we only sent out records where we did not already have a good phone number (at least per the coding in our system of record).
Even then, we did not append the phone numbers to our system of record, but only to the calling system database. Then the phone number would get pulled into the system of record when the calling program received a gift or pledge (on the theory that contact was made, and the caller was able to update the phone number if, for example, they got a recording with a forwarding number). At the end of the campaign, we loaded the phone numbers for refusals or other cases that indicated that we made contact with the constituent, even if there was no pledge.
My US$0.02 worth; the usual disclaimers apply.
Good luck!
Alan
Alan S. Hejnal (he/him/his)
Data Quality Manager
