Not sure about your exact model of VOIP, but I have had many issues with VOIP's going offline then the next day comming back online!
This is usually a fault of the actual VOIP hardware box, but to get it through the VOIP suppliers support personnal is very difficult.

I would suggest that you contact your VOIP account business and explain that nothing has changed, but it doesn't work.
They will then ask you to run reset commands through the VOIP (plus all the turn off for 20 minutes stuff) And then reset up the VOIP settings again for you.

This may in fact work. But if it happens again I would ask for replacement box, which will resolve it, for at least the next 6 months.

If the VOIP phone is not the supplied phone from your service provider, just one you picked up. Find out if it has a warranty. You may see that I am leaning towards hardware related here.

 

thanks for the help but i think my issue is going to be much bigger since i've learned from the isp that they are pretty much blocking the use of vonage over here. a soldier can't get a break with them blocking the isp.