Ooma Forums

So if your internet service drops for an extended outage, is the only way to route calls to your cell phone by having Ooma Premier and setting it through the website?

Pretty much... Unless you just do multiring you'll have to do this manually if your ISP goes down since they don't have failover as of yet.

http://forums.ooma.com/viewtopic.php?f=6&t=1864

If you just have the core services, you can setup a voicemail notification to your email/SMS on your cell phone. You'd then be able to check voicemail from an alternate internet connection if available or when your internet connection returns or by calling your ooma number from your cell phone.