99% of the time, the answer is 

The problem with sharing voice and data is you have no control over how the line is being used. If three other people send an email while you are on a voice call using the same line. Your conversation will disappear momentarily, break up or sound like speaking underwater. 

Another reason we do not like sharing voice and data is that you have to use a data ISP. This means your voice traffic will be routed over a third party network, which may have congestion or non-prioritisation of voice traffic. In simpler terms, we have much less control over where your voice is travelling, so there is a much higher chance of having quality problems.

The only time the answer is yes is when you are using a single extension at a remote office location such as your home or satellite office. This is not guaranteed to work, but since there will be such low use on the line, it will likely work perfectly most of the time. 

We would say yes because only a person affected on a specific day cannot be contacted on the office extension due to the ADSL line being down or congested. It is quite easy to contact this person on a mobile phone, and they may simply make calls on via mobile until the line is back to normal. We see these single extension offices as a perk of the cloud PBX, 

If your satellite office is mission-critical, then we suggest ordering a dedicated voice line from Euphoria Telecom with built-in failover in the case of a disaster.