I've recently started receiving (to my mobile on a UK registered Vodafone
account) some intermittent non-speaking calls from numbers such as '+1819'
and '+1822' etc.

Does anyone know what these numbers are? Are they the first part of a US
phone no. (country + are code)? Or something else? (Perhaps SMS mailbox
nos. phoning me, if that's possible?)

Has anyone else received similar nuisance calls, where the other party just
doesn't speak?

(I'm not confusing these with mis-connected autodialler calls, where an
operator doesn't get connected. These calls either come from a recognised
number or have number withheld.)

See More: Nuisance calls from +1819, +1822 etc.