At first must specify if want to use GSM or SMPP links?
If you want to use SMPP links, please contact one of the
VAS(=Value Addes Services) provisers, Magfa, Rahyab or
Atied Dadeh Pardaz. but if you want to use GSM, you must
enable your PC with GSM Modem. About sample  code,
just google this. I hope you will find a lot!

you need to have an sms  gateway in between,

JavaPhone's Datagram API supports SMS sending through GSM, WDP and UDP, but receiving of SMS messages only in WDP and UDP. You mentioned "simple message" . Does this have to be SMS? could the communication be over bluetooth or does it have to be long distance (over 100 m) ?

the best way to start is to look into the developer site of the phone's vendor, and look into their supported APIs. you will see loads of samples. someone had posted the same question while ago, if you find into the history of the messages here, you will see the answers, articles and sample  codes.

also few links from my favorite's bookmark:
http://www.developershome.com/sms
http://www.developershome.com/sms/freeLibSMS.asp
http://jsmsengine.sourceforge.net/installation.php

http://www.its4sms.com
Its4sms.com/sendsms.asp
http://www.dreamfabric.com/sms/

www.wirelessdevnet.com/.../