Do's and Dont's

[GoneWithTheWindows]

Don't do that.
Run 2 dedicated lines. If you run a single line then the Voip phone is in line and then your gigabit network is limited to 10/100.

Also the Voip line acts as a backup data line should something break (and things do break).

Not true at all.
VOIP Deskphones come with GB NIC's now...

 

[clickingbuttons]

Why CAT6?

CAT5e can easily do 1gbit at 100meters, no real point running CAT6 imo

 

[MDKza]

Why CAT6?

CAT5e can easily do 1gbit at 100meters, no real point running CAT6 imo

Because of multiple things like crosstalk and 10Gb capability. CAT5E is fine and will work, but you might as well do CAT6.

 

[Bash crash]

Ran a similar project not too long ago...
Multi storey building - 4 Floors
Dedicated a switch per floor with a single Cat6 per point running both Data and VOIP.

Had a company to do the implementation.
Went with the Grandstream PBX VOIP solution
Used SEACOM as ISP - a lot of other companies tried selling others but contention ratio was my concern and SEACOM was the only who could assure a dedicated line.

All went well and still working great 8 months later...

 

[Thor]

Voice VLAN + Data VLAN single cable. No need for 2 cables per desktop.

EDIT:
Just replied without reading comments fully.
It appears some users are living in the 2000's still.

You definitely do not need 2 cables.
Have voice and DATA on the same port.
Shielded CAT6 cable if you are running over electrical wires.

Always run two cables.

 

[MDKza]

Always run two cables.

Let's agree to disagree

 

[Thor]

Fair