You may want to try TCPMP or CorePlayer.
According to the Pocket PC Media Chart at
www.feederreader.com/mediachart.html , TCPMP on the Pocket PC is able to play Vonage voice mail files, which are in CCITT-u-Law (Vonage) format.
I would hope that because TCPMP on the Pocket PC is able to play them, then TCPMP on the Smartphone is able as well.
I'd love to update the chart indicating Smartphone versions of players, but there's very little discussion here of media players specifically for Smartphone. Plus I'm afraid that Smartphone versions might be cut down from their Pocket PC versions and the chart would therefore be less useful. Thoughts?
Greg Smith
Author, FeederReader - Windows Mobile news, blogs, audio, video, podcasts downloaded direct to your Smartphone or Pocket PC
www.FeederReader.com - Download on the Road