Pynchon's voicalick profile Ax him to say, Aks him to say Ask

[Terrance]

"ax" is the original Old English pronunciation  
of the verb.  Already in Old
English the reversed order "ask"  
("sk" instead of "ks = x") was used by
many people, but "ask" never succeeded in 
totally eliminating "aks" for
all English speakers.  Throughout the subsequent 
history of English we find
speakers and writers who use "ax".  It 
is the form used, in the spelling
"ax", by William Caxton in 15th century 
England.  Caxton was the first
printer of English, and recognized the
 problem of variant forms of
English and of what to select to reach the 
largest audience.  In his time and
place "ax" was such a normal pronunciation 
that he did not hesitate to use it
inpublishing, and did not even consider 
it a particular problem , given
much more serious problems like whether to 
use "eggs" or "eyren" (as you
guess, "eggs" later won out over "eyren"). 
Although later publishers selected
the "ask" form, "aks" remains the usual 
form in speech in some areas of
England and also in the US.  Once 
authorities selected "ask" as the official
form, at the expense of "ax", it became 
"non-standard" and thus a marker of
varieties of English less influenced by 
the written standard and the
educational system that insists upon it.  
The colloquial English spoken
by perhaps the majority of African 
Americans is only one of many varieties
in which the ancient "ax" pronunciation still survives.
Some particular pronunciations have 
low prestige ("ax" for ask or "liberry"
for library), but pronunciation has not been institutionalized—there is
no standard American accent.

http://college.hmco.com/history/readerscomp/rcah/html/ah_051600_language.htm