Translation help please

There's a sentence in my language book that I can't quite understand...

"Sumimasen, Yamada-san no denwa-bango wa shitte imasu ka"

Could someone please translate that for me?

"Do you know the telephone number of Mr. Yamada?"

The Japanese sentence might be: Sumimasen, Yamada-san no denwa-bango WO shitte imasu ka"

Excuse me. Do you know Mr./Mrs./Miss/Ms. Yamada's telephone number?

I agree that if the textbook introduced the structure "....wo shitte imasu" for the first time, then the typical textbook style sentence would be with the "...wo," but the sentence in the original question is also valid: "Yamada-san no denwa-bango WA shitte imasu ka."

Maybe that's why the original poster got stuck with this question?

The sentence with "...wa" is well possible in a dialogue like the following, for example (suppose you call an office and ask for Yamada-san):
- Sumimasen, Yamada-san wa imasu ka? (Excuse me, is Yamada-san in?)
- Kyou wa o-yasumi desu. (Today it's his/her day off.)
- Kinkyu na no desu ga, Yamada-san no denwa-bango wa shitte imasu ka? (This is urgent, do you happen to know Yamada-san's phone number then?)

Meaning, now the caller knows the *whereabouts* of Yamada-san, so now the topic/interest is about the *phone number.*

So the sentence literally is more like "When it comes to Yamada-san's phone number, do you know?" (But normally translation into English would be: "Do you know/happen to know Yamada-san's phone number?")