Phone model?

 

My phone occasionally changes the ringtone and notifications to "Silence". You could check that I suppose. That could make it seem like it was going straight to voicemail. I can't remember now what app I finally found was doing it, but it wasn't actually the phone itself but something 3rd party.

So.. I think that is in settings.. Sound and Display... phone ringtones and Notifications ringtones... to have a quick look.

 

You didn't just port your number over from another carrier recently did you?

 

I think there could be two main reasons for this.

You might have downloaded an app that has Phone access and it is causing phone calls to transfer straight to voicemail. Go to [Settings>Applications>Manage applications] then select an application and scroll down to view the permissions. In other words a software issue.

Or the other possibility is to do with the hardware. Is it possible that you are not always on 3G? I have read that ACS Alaska has the "best" 3G coverage in Alaska but I can't be sure if that's true in the area you live. If you lose reception to your 3G network it will fall back to your 2G network. While being on a 2G network you will not be able to have voice and data at the same time(Although voice calls are the priority). While on your Milestone desktop keep track of the symbol indicating your network type to ensure you're always on 3G.