There are MANY more Yearbooks beyond just 1957-1958 on that site. (1957-1958 may be one of the most interesting years as far as TV is concerned though)
BAldwin3-1234 is the same as 223-1234.
I'm on slightly weak ground with my knowledge below, so take that into account, but...
When telephone service was initially launched, you couldn't automatically dial another phone. You picked up the phone, and an operator answered. You told the operator who you wanted to talk to, and the operator put in a patch cord between your phone and the phone of the person you were calling. Of course, each of those phones had a number.
As phone service became more popular, it became impossible to put every phone in the city on the same switchboard. Multiple telephone "exchanges" would be built around the city. If you wanted to talk to someone on a different exchange, you asked your operator for "Baldwin 3 - 1234". She'd send your call to the Baldwin exchange, call the operator there, and ask them to patch you to 3-1234.
As exchanges became equipped to allow callers to dial their own calls, numbers were associated with the exchange names. If your exchange could auto-dial, you just dialed 223-1234; if it couldn't, you had to ask the operator.