Seeaye elsee youel eighty ee - tee hay chee - ess youem - esseye ecks - pee el youess - ess eevee ee en.

you ess ee - tee aye chee - ess aye emee - see ohdee ee - effo are - are ee essyou eltee ess.

(In reply to answer by K Sengupta)

At the outset, we observe that when we spell out the string "Hay Che
Aydee - Aysee Hay Che", as given in the problem title, we obtain the
word "HEAD-ACHE".

Now, we observe that the pronounciation of the letters in the said
title differs slightly from the corresponding pronounciation in terms of wikipedia.
(Reference:http://en.wikibooks.org/wiki/English/English_in_use/Orthography)

Accordingly, spelling out the words inclusive of the problem text,
we observe that the following words stand for these letter/ letter
combinations. 

Word    Letter/letter combinations

Seeaye    CA
elsee       LC
youel       UL
eighty      AT
ee           E 
tee          T
hay         H
chee       E
ess         S
youem    UM
esseye    SI
ecks       X
pee        P
el           L
youess   U
ess        S
eevee    EV
ee         E
en         N
you       U
ess       S
ee        E
tee       T
aye      H
chee     E
ess      S
aye      A
emee   ME
see      C 
ohdee  OD
ee        E  
effo      FO
are       R
are       R
ee        E
essyou  SU
eltee     LT
ess       S

Accordingly, upon decryption after duly adding the necessary punctuation including the period, we obtain the following sentence:

"Calculate the sum. Use the same code for results."

In accordance with the first sentence, performing the addition of six(6) plus(+) seven (7), we obtain thirteen, which is the spelled out form of 13.

Consequently,the secret message is 13 or "thirteen" in the spelled out form.

Edited on May 6, 2008, 2:22 pm

Posted by K Sengupta on 2008-05-06 05:07:42