[yttribium]

Did you know that within living memory there was an entire network of anonymous telephones you could pay for with untraceable cash in five cent increments?

[Eddy_Viscosity2]

As I recall, these could be 'traced', but you have to keep them talking long enough for it to work.

[josephcsible]

The payphone itself could be traced, but not the identity of the person talking on it.