  The technique of frequency phase transfer (FPT), enabled by multiband
receivers with shared optical path (SOP), is set to become a true backbone of
VLBI operations at frequencies above 22 GHz. The FPT has been successfully
implemented at the Korean VLBI Network (KVN), while gaining ever more prominent
attention worldwide. Over the next few years, FPT VLBI at 22/43/86 GHz will
become feasible at more than ten telescopes in Eurasia and Australia. This
development would bring order of magnitude improvements of sensitivity and
dynamic range of VLBI imaging at 86 GHz and deliver astrometric measurements
with an accuracy of one microsecond of arc. The resulting exceptional discovery
potential would strongly impact a number of scientific fields ranging from
fundamental cosmology and black hole physics to stellar astrophysics and
studies of transient phenomena. It is now the right moment for establishing a
Science Working Group and a Technical Working Group for FPT VLBI in order to
actively focus and coordinate the relevant activities at all stakeholder
institutes and ultimately to realize the first global FPT VLBI instrument
operating at 22/43/86 GHz.
