In my case, the existing router is at the demarc inside the house, so connecting and testing at that point should be no problem. I will be here when the install happens, so I don't necessarily expect problems working with the installer. Comcast's techs were always very good and accommodating, but I have less confidence in the consistency from Verizon.
The reason that I'm asking about the ONT, etc. is that my basement is finished and the demarc point as along a wall directly behind a standard 2' 8" door (along with the electric service panel). There is perhaps 4 inches of clearance behind the door. There also isn't much room to fish wires down from the outside, but I suspect that there should be enough. The existing ingress/egress for the electric, telco, cable is above that door but mostly inaccessible except for a one-inch or so gap between the door jamb and the wall. I'm assume they've dealt with similar in other homes, I'm just trying to prep the best I can. I get nervous when other people start drilling and digging on my property.
My neighborhood was "wired" for FiOS about a year ago or so (conduit and vaults in the ground). However, I have yet to find a neighbor who has FiOS service.
JKG