Is it possible to use agile on projects where scope is known upfront? Yes.
Is it the best approach? Maybe.
It all boils down on how much uncertainty you'll face along the implementation and how much value you can deliver incrementally.
For instance, when setting up a video conf project, do you know...
- whether the network will be capable of supporting the new demand?
- this new demand will be stable across different offices?
- in case you need to change your network provider in a given location, are you aware of how to proceed with it?
If all the above is going to be delivered "by the book", then go with waterfall. On the other hand, you may find benefits on the incremental approach agile delivers, as you can setup an initial part of the structure for a few offices while you address the problems on other offices.
Take this with a grain of salt - agile is about incremental deliveries. If there's a hard committment date (due to any external factor, for instance) you may want to stick to the Waterfall that will give you more capacity to cover your part of the project from eventual external dependencies.