I think the OP is answering the question themselves?
a) Old fashioned phones were much less susceptible to interference from
strong radio signals; if this is what the 'Crosstalk' is. Those older phones
were simple, contained very little electronics, were rugged, tested and
designed to the international standards of developed countries for
performance and not that cheap. Time was when one had to get at least one
main phone from the monopoly telco! Then finally the customer could get
their own phone plug it in and just rent the line from the telephone
company.
Saw one case where a customer was trying to dial on a Canadian telephone
line with an 'antique' phone they had brought back from a trip to France
which had a completely different rotary dialing speed and percent make-break
signalling pattern. Wouldn't ring on incoming calls either IIRC. Wondered
why it wouldn't work!
Or b) If the new phone is a cordless type phone with a handset you can carry
around without wires it may be picking up somene else's cordless phone
conversation? Seen that also; kinda funny when you pay the long distance
charges for a call made by that 'other' phone! Not likely though, today with
a good quality digital cordless.
Or c) It's just a cheap and nasty
20to30 phone; many horror stories
about those! Some almost tragic. Cheap phones often contain electronic
components that are susceptible to picking up interference. A line powered
phone may well be an indication of internal electronics?
Back in the days of Bell telephone etc. having a monopoly etc. they had
fixes for item a) and felt responsible for all aspects of service.
Today anybody can buy an el cheapo phone not built to any particular
standard and plug it in and somehow the major improvements made to the
telephone networks during the last fifty years manages to cope even if the
phone isn't that good!
But hey ain't competition wonderful?
PS I don't blame the telcos for charging $45+ an hour for dealing with some
of the junk telephone gear that is sold and attached to telephone lines!