Cabbies tend to treat Radio as a direct-connect telephone. As far as it goes, it's a private "circuit" they're on and in a lot of operations, they pay for their pset on that circuit......why wouldn't they feel free to gossip on spare bandwidth?
Regarding "Roger" the following can be punctuated to make perfect sense.
"Does roger roger roger roger roger roger roger rogers roger rogers roger rogers rogers roger rogerson."