Order telecom services for your new location.  Double check if there’s been similar services in your suite.  I recommend ordering services 2 to 3 months before moving (45 days is absolute minimum).  If it is a new building, there’s a slim possibility that the phone company does not have cable underground to the building’s main demarc.  In this case, they are required to provide the installation; however, they have their own time frames.  You don’t want to move a company, then wait for Internet and/or phone service for 30 days, as an example (I’ve seen longer).

Are cubicles (modular funiture) involved with your new office space?

Schedule meeting with architect, IT personell, and structured cabling installation company such as Tier 1 IP to make sure all questions are answered.

Decide if it is time to upgrade your phone system.  How old is your current PBX?  Does it make more sense to install a new VoIP system instead of moving your existing phone system.