Commercial letters

Hi everyone ! Long time no see!
What is wrong with this letter sending out to its agents as well as clients by TDC?

Dear Sir/Madam,

CEPA is creating enormous business opportunities for thousands of Hong Kong service providers.
But now how do local service providers make the most of this unique chance to expand their business onto the mainland?
Hong Kong Trade Services magazine is the best channel to maintain close contacts with 55,000 SMEs!
Please refer to this brochure for details or call the enquiry hotline at 1830 668

We look forward to being of service to you.

Yours sincerely,
Publications Department
Hong Kong Trade Development Council

[Tdol]

I'd say 'on' with a phone number and sign off with 'Yours faithfully'.

Thank you Mr. Tdol! You are my real English teacher for nothing.

I understand that if using Dear Sir/Madam,
the ending should be used Yours faithfully.
But if we use Dear Mr. Tdol, Mr Ronbee, or Miss Casiopea,
We should enclose the letter with Yours sincerely,
How about Yours truly?

Regarding the telephone number, we usually use at. I am still pondering whether it is correct or not!

[RonBee]

That letter looks perfectly fine to me. Is the question about the closing?

:?