This is only a partial solution, a first step. The letter is written ...
in English, at least part of it. It uses a monoalphabetic cipher where Greek letters and other symbols represent Latin letters. The letter uses abbreviations such as u = you and bcos = because. Punctuation is as usual in English and when we assume that the word with the apostrophe in the second line is either "can't" or "don't", we can guess that the first sentence reads:
I don't think that I would b able to call u again.
The whole letter reads:
my muthu
I don't think that I would b able
to call u again. bcos n.n last
vilichitt shelf properly close
cheyythilla. so avarkk manassilayi
n.n vilichinenn. moreover phonil
ninn balance. kurannathum avarkk
manassilayi. so if u don't mind will u
give me a phone. ennala veetil
full preshnam aayirunnu. so inorder
to solve it, n.n sammathiciu n.n
phone eduth ninghale vilichini but
n.n parannu n.n ellam nirthi enn
parayananu vilichathenn. appune nalla
vishvasamanallo. athko.d n.n parannu
n.n oolude mumbil nilla vilichu paran
enn. oolum sammathiciu enghanayallo
and at last they believed. but
avarkk pediyund n.n ellam nirthu e?
parannathkond whether u would take
revenge on me. achan ene oriknasum
ninghala that shopul kanaruthe.
bcos he told eneyum oonn nilla
disturb aakunundengil case edikkam
karanam avarude vicharam n.n
ellam parannu. kainnittum backil nadakura-
nenn. ene muthal appukk half day class
aanu. n.n oolude kaiyil letter
kodukk.a. n.n vandu-moonuu days aayi
letter kodukhunnu. but she told
u was not there. n.n ene enkk
pattumengis mathre viliku ketto.
don't think anything. n.n ene athava
vilikunundengil new numberil mathre
vikikku pinna phone ennuk after onam
vacationu. shesham mathi enkk pediyu-
nd but enkk vilikan. vera no other
method. if u have some problem
then no need eykk kure parayanund
but epposhum vilikumb. enthenghlum
preshnam undakam.
enkk orupad orupad orupad
eshttanu ketto
yours lovingly ...
I've tried to keep the layout as in the original. Thanks to elias and noteness, who have contributed in the comments below, I now know that ...
the non-English words are Malayalam. This language has its own script, but in the letter it is transliterated into Latin. I'm obviously not familiar with Malayalam, so there may well bet transcription errors in the Malayalam words. Sorry about that.
For completeness's sake, the alphabet is
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
α β γ δ ∞ 6 ρ x λ . π σ μ ν ε Σ . ω φ ψ Λ Ω ~ . τ .
(The τ (Y) isn't really a τ, but more like a latin t. The ν (N) could also be a θ. The dot in n.n stands for ya and the word, which occurs often, is nyan/ñan, or I in English. Two letters are unresolved: the t with the stroke to the left in athko.d and the u-shape in kodukk.a.)
