Your Cable Company
Many people still have home phones or business phones that are probably bundled through their Internet service providers. In this case, being able to access your digital phone service is important too, especially if you spend a lot of time away from home or the office. The big three in cable services - Qwest, Comcast, and Cox - each have their own separate downloadable apps that allow you access to not only your digital voicemail, but your account and even your TV.
Cox has their mobile connect, which is still being issued to their customers in various states, so if you're a Cox customer, you'll need to ask a representative if your area is serviceable with the app.
Comcast has their Xfinity mobile widget that allows you to view your email inbox, your voicemails, and even the listings for your TV.
Unlike the other two, Qwest only has an app for subscribers of their Qwest Home Phone and Voicemail services. The widget is fairly simple, showing how many messages you have, as well as who left them for you. You can also use the app to forward your home number to that of your cell phone.