Gramogram

A gramogram or grammagram or letteral word is a letter or group of letters which can be pronounced to form one or more words, as in "CU" for "See you". They are a subset of rebuses, and are commonly used as abbreviations.
They are commonly used as a component of cryptic crossword clues.
A poem reportedly appeared in the "Woman's Home Companion" of July 1903 using many gramograms: it was preceded by the line "ICQ out so that I can CU have fun translating the sound FX of this poem".
A restaurant scene where a customer initially asks "FUNEX" ("Have you any eggs") appears in a 1949 book "Hail fellow well met" by Seymour Hicks and was performed in "The Two Ronnies" under the title "Swedish made simple".
The book "How to Double the Meaning of Life" devotes three pages to gramograms, to which the author, Anil, gives the name letteral words.
 neither spelling of the word appears in the online "Oxford English Dictionary".
Some are homophones because some can be used for multiple words.
Examples of words.
1: depends on dialect
2: when pronounced "Zee" and not "Zed"
Examples of names.
1: North America
2: when pronounced "Zed" and not "Zee"
Examples of suffixes.
1: only used for names
2: depends on dialect
Examples in arts and culture.
The Marcel Duchamp "readymade" L.H.O.O.Q. is an example of a gramogram. Those letters, pronounced in French, sound like "Elle a chaud au cul", an idiom which roughly translates to "there is fire down below". 
The William Steig books CDB! and CDC? written mostly in gramograms. 
The suicide prevention charity R U OK?'s name is a gramogram, with supporters encouraged to text "R U OK?" to friends and family to see how that person's mental health is going.