Yes, it is true. This FAA page has more info.
The Very High Frequency Omni-directional Range (VOR) Minimum
Operational Network (MON) provides a conventional navigation backup
service in the event of a loss of Global Positioning System (GPS)
signal. The MON includes the minimum number of geographically situated
VORs in the contiguous United States (CONUS) necessary to provide
coverage at and above 5,000 feet above ground level. Additionally, the
MON supports International Oceanic Arrival Routes and mission critical
From the Federal Radionavigation Plan the Gerry references in the comments:
ILS is the standard precision approach system in the U.S. and abroad.
FAA operates more than 1,200 ILS systems of which approximately 150
are CAT II or CAT III systems. In addition, DoD operates approximately
160 ILS facilities in the U.S. Non-Federal sponsors operate fewer than
200 ILS facilities in the U.S.
As the GPS-based augmentation systems
(WAAS and GBAS) are integrated into the NAS, and user equipage and
acceptance grows, the number of CAT I ILSs may be reduced. FAA does
not anticipate phasing out any CAT II or III ILS systems.
The NAS includes more than 1,300 NDBs. Fewer than 300 are owned by the
Federal Government; the rest are non-Federal facilities owned
predominately by state, municipal, and airport authorities.
FAA has begun decommissioning stand-alone NDBs as users equip with
GPS. NDBs used as compass locators, or as other required fixes for ILS
approaches (e.g., initial approach fix, missed approach holding),
where no equivalent ground-based means are available, may need to be
maintained until the underlying ILS is phased out. Some NDBs may also
need to be maintained to facilitate training and proficiency
requirements. Most NDBs that define low-frequency airways in Alaska or
serve international gateways and certain offshore areas like the Gulf
of Mexico will be retained.