I'm pretty sure a crafty spook-geek could transform your average desk phone into a handy-dandy surveillance "bug".
...as was done to the "direct line" phones to the Pentagon that were on the desks of many state governors in the 60s. This was first found during the early 70s in the governor's office in MD.
AT&T at the time claimed it was a "mistake in wiring" (roll eyes)
A corrupted ‘Smart TV’?