In general, 911 calls cannot be reliably made using a VoIP service. But VoIP providers in the United States are under a looming deadline to make it possible to dial 911 and reach the appropriate emergency call center. That capability is several months away, however. Most VoIP operators suggest keeping a cell phone on hand just for emergency calls. The exceptions are VoIP services provided by cable operators, all of which have the appropriate agreements in place to supply what's known as "enhanced 911."