Use the phone account when checking if a number is a voicemail number.

Currently when checking if a number is a voicemail number, we are checking
it against the voicemail number of the default phone account, which
results in a non-default voicemail number incorrectly being identified
as a regular phone number.

Bug: 17925501
Change-Id: Id73ff399467e2446a58c58e6211d1ec1d1f20b30