There are only two stories indicating there is a telephone at 221b Baker Street with no mention of a phone number.
In 'The Adventure of the Three Garridebs' Holmes calls Nathan Garrideb to setup an interview at Garrideb's home.
In 'The Adventure of the Retired Colourman' Holmes says, "Thanks to the telephone and the help of the Yard, I can usually get my essentials without leaving this room."
Both of these stories are late in Holmes' career, so it is likely the phone was a late addition.
NOTE: If you are referring to the 'Sherlock' BBC TV series, your question is in the wrong category.
I would start a search at the link below for I believe they still answer snail mail for Sherlock Holmes.
Sherlock Holmes is a fictional character dummy!
The Address is 221b Baker Street
Sherlock Holmes' real name is Sherlock Holmes.
North West, possibly.
Sherlock Holmes
Robert Downey jr has been in two Sherlock Holmes movies: Sherlock Holmes (2009) and Sherlock Holmes: A Game of Shadows (2011)
Nothing. This is the fictitious address of Sherlock Holmes. Actually, it is the current address of the Sherlock Holmes museum, and lots of events happen there. Check it out if you can.
This is because the author, wanted to make Sherlock Holmes sound realistic enough for people to not think that he was fictional.
The Address is 221b Baker Street
Sherlock Holmes' real name is Sherlock Holmes.
Sherlock Holmes 3
221B Baker Street, the home of Sherlock Holmes.
North West, possibly.
.... Sherlock Holmes
Sherlock Holmes.
Sherlock Holmes
"Young Sherlock Holmes" (1985). Stars Nicholas Rowe as Sherlock Holmes, Alan Cox as John Watson.
221B Baker Street, Marylebone, London.