You can also do some simple math to calculate exactly how many VoIP lines your internet connection can support:
Multiply your upload speed by 1000. This converts the units from Mbps to Kbps, so if your speed is already expressed in Kbps then skip this step.
Divide your result from step 1 by 445. This will tell you the recommended number of phone lines your connection can support.
Divide your result from step 1 by 100. This is how many phone lines you can support in a perfect world where your internet connection was stable and consistent and no bandwidth was being used for other activities, like browsing or downloading.