Is the voicemail one that comes on it default the verizon one? I thought it was the sense one and free
Free Verizon Voicemail is what every Verizon number has. The messages are stored on Verizon's servers, not downloaded to the phone. When you dial your number, or dial *86, you are billed for airtime as you connect to Verizon. You then can listen to your messages.
Verizon's Visual Voicemail actually pushes the recorded messages to your phone, where you can view the caller info, as well as listening to each message, in any order that you desire. AT&T includes VVM on all iPhone plans, but the greedy folks at Verizon feel as if they are justified in charging $2.95/month.
Youmail is free, and works much like Verizon's VVM. When you set Youmail up, you initially dial a number that re-routes unanswered calls to Youmail's servers. Audio messages are then pushed to your phone via your unlimited data connection. Youmail gives you an alert, you may then open the app, (I put the icon on my home screen), and view and listen to your messages.
Youmail also allows you to upload your contact list, so if you use their pre recorded messages, the system actually names your caller by name, which really freaks some people out. My wife thought that I had a girlfriend, the first time she left me a message
For a small monthly fee, Youmail will also transcribe your messages, and sends them to you in text or email.
If you end up not liking it, you can always uninstall it.