The easement might be public utility easements on public streets, so the original subdivision map might bear the roadway and easement dedications.  So, an easement can go back many decades. 

 If the easement crosses or is upon private lots, then it might be proscribed by an agreement or deed of record, and the verbiage of that instrument can be equally crucial to understanding rights of the parties involved.

 In many cases as with the free wifi movement, these sorts of devices are being set up by agreement with homeowners and landowners, hence creating new property easements.  Unlike the free wifi people who hang an antenna out of their apartment window for anyone to tap into the internet, these cellular companies are gaining access through the more traditional arrangements, although the article failed to mention this.

Yes, easement research could be needed.  It's a case by case basis.  Public works, municipal utility departments, subdivision maps, and GG Index easements have all been used by us to find easement matters of this sort.  While the former two are outside the standard title search parameters, they have been useful in establishing such matter, to the gratitude of our clients for going "above and beyond".  Naturally, we provide disclosures and disclaimers of liability in our reports as we annotate such additional work as no-fee, courtesy matters that do not create liability on our part for noting.