Can't you just define a new user in elastix, and define a new group such as "voicemail" and just let that group see their voicemails? Once you define both, you need to make sure that the user belongs to the group voicemail. Login as them and it works fine.
Browser choice? I've had all kinds of issues with different browsers and how they operate with different products. Internet Explorer seems to be the worst offender. Firefox is my current best option. Google Chrome looked great, but some of the forms do not get rendered as expected. Good Luck!