You posted elsewhere too....
In FreeDigits
Are you entering exactly this:
sip:123456@voxalot.com
try this instead(no sip in front):
123456@us.voxalot.com
Can you tell which voicemail you are going to, is it VoXalot or FreeDigits (they have their own Voicemail, and most times even when everything is working properly, you'll receive calls to VoXalot, but after about 4 rings you'll go to their voicemail)
Also call your voxalot account (as I mentioned in that other thread) and see what happens.