For SMS/Voicemail separation, how about an option like you do for contacts. At the top, let it be selectable for sms, voice mail, or BOTH.
For voice mail playback, can you somehow scrape the link to the voice mail so it is launchable though Dialcentral? Maybe not stream the audio through DC, but allow it to launch your browser to listen to it.
Also is there any way to make the downloading of contacts in the login process optional? For the most part I use DC for SMS receive/reply. While it doesn't take long to download the contacts, for the most part it is unnecessary for some users. I rarely change my contacts as I assume many others are the same way. Can you somehow cache the contacts to a local file, and only update it with a refresh within the application. It will speed up the login process and eliminate a redundant process (for me at least).
Better yet, maybe a selectable option for the user to select their "home screen" when they launch the application. So if you are a texter like me, opening the messages tab on the boot.