Enable use of phone accounts for voicemail info display.

Call the "isVoicemailNumber(subId, number)" method instead
of the one with just the number. This is because we need to check
whether a number is the voicemail number for a specific phone account,
otherwise the UI would never correctly display "voicemail" for the
non-default SIM.

Bug:17925501
Change-Id: If1d6cb1acfcb570aca5e639858af8804bac202c0