Is there a term for advertisers use of deliberately misspelled words (e.g., Lite)?

How about "commercial spellings"?

"Be on the lookout with your child for examples of spelling errors in
print material--newspapers, signs, advertising brochures. Gather
examples of 'commercial spellings,' such as lite foods and brite
detergents."

New Albany Plain Local School District
http://www.new-albany.k12.oh.us/district/curriculumK-8/SittonSpelling/proofreading.html

"There is something odd about your server here. It does not like
commercial spellings, such as 'lite.' Oddly, when I use lite in the
text, it works! Unfortunately, when I created the email address, I
used the way the beer is spelled in most commercials and the labels. I
know it is a misspelling, but what the heck."

Lease2Purchase Message Board
http://www.lease2purchase.com/wwwboard/messages/3211.html

"Other commercial spellings are achieving widespread usage in casual
writing (at least in the US), such as 'lite' for 'light'."

alt.usage.english newsgroup post
http://groups.google.com/groups?selm=57s8l5%243qu%40krypto.zippo.com&oe=UTF-8&output=gplain

A more technical term is "metaplasmus":

"Metaplasmus --a type of neologism in which misspelling a word creates
a rhetorical effect."

Homepage of Dr. L. Kip Wheeler 
http://guweb2.gonzaga.edu/faculty/wheeler/schemes.html 

"Metaplasmus: A general term for orthographical figures (changes to
the spelling of words). This includes alteration of the letters or
syllables in single words, including additions, omissions, inversions,
and substitutions."

Brigham Young University
http://humanities.byu.edu/rhetoric/Figures/M/metaplasm.htm

"You have only really misspelled a word if you did it by accident. 
That is the lesson you learn from the rhetorical figure called
metaplasmus.  Metaplasmus is the intentional misspelling of a word for
rhetorical effect."

Memoria Press
http://www.memoriapress.com/newsletter/news1101.html

Search terms used:

"advertising" + "misspelling"
"advertisting" + "misspelled"
"metaplasm"
"metaplasmus"

I hope this information is useful. If anything is unclear, or if a
link does not function, please request clarification; I'll be glad to
offer further assistance before you rate my answer.

Best wishes,
pinkfreud

Some of the links were not helpful but overall I learned a few things.
It was better than I was able to do on my own! Thanks!

I am sorry my answer disappointed you.

I have asked the editors to withdraw it so that you will not be
charged.

In the future, please remember that if an answer is not fully
satisfactory, rather than giving it a mediocre rating, you have the
option of requesting clarification so that a Researcher can try to
zero in on the exact information that you desire.

~pinkfreud

I didn't say I was disappointed. I thought 3 stars was a good rating.
No need to withdraw it. I was happy to pay you. This is my first time
and didn't realize you would think 3 stars was disappointing.