Sometime in Mid-2009 YouMail quietly introduced DropBox. DropBox lets you send email notifications from other voicemail services to YouMail. I use the same service from PhoneTag and it is actually pretty useful. YouMail DropBox converts the voicemail notifications sent via email from another service provider when it is sent to [email protected] (where YOURNUMBER is your 10 digit phone number).
The email notification from your service provider must include the audio file attached. Currently YouMail DropBox supports: Vonage, MagicJack, Google Voice, RingCentral, Phone.com, eVoice, OOMA, and Packet8.