As soon as I Switched to Verizon Fios more than 5 years ago , My Home Wireless Intercoms STOPPED WORKING.
The Individual Intercoms purchased from Radio Shack worked very well , One in each room and they plugged in into the household electrical wall outlets , voice was carried via the house electrical system.
The only FIOS items Plugged in into the Household Electrical are The FIOS Panel , One Moden and One WI-FI Extender which I added 2 years ago.
Has this happened to you and how did you fixed it ?
FIOS equipment won't affect service if it is via electrical wiring no ore than any other device.
To make sure, disconnect all FIOS devices.
Then see if intercoms work.
If they do, then plug FIOS devices in one at a time and test intercom.
Are you certain that Intercoms communicated via electrical wiring and not via RF?
Look on the name plate of one of the Intercoms and see if there a mention of a frequency.