SMS Centre
SMS Centre is a 32-bit client for sending SMS messages to mobile phones or SMS/Paging Messages to any worldwide network whose dial-in service center supports the TAP protocol. This program uses a landline connection to the SMSC (Short Message Service Centre) to send a text message of up to 160 characters to any Mobile Phone that is capable of receiving Mobile Terminated SMS. SMS Centre is TAPI-compliant and requires a properly installed TAPI Device. SMS Centre has an intuitive interface that requires minimal knowledge or skill. A simple address function is included for frequently called mobile numbers, and messages can be broadcast to group members on different networks. OS: Windows 95/98/NT
File Size: ~ 2MB Free to try

SMS Manager - Get your hands on SMS Manager, and discover the beauty of SMS right on your computer screen. Read, reply, forward, and send messages to your friends, all in a user-friendly environment.
OS: Windows 95/98/NT/2000
File Size: ~ 1.5MB Free

Oxygen Phone Manager (Nokia 8xxx GSM Phones)
Read, edit, store, load, and rewrite data with your Nokia phone.
OS: Windows 95/98/NT/2000
File Size: ~ 3MB Free to try

WildSMS - Send short text messages (SMS) or Flash SMS messages from most PCs to most mobile phones via your Internet connection. You can also send ringtones, logos, and picture messages with text attached from your PC to most Nokia, Sagem, and newer Ericsson mobile phones.
OS: Windows 95/98/NT/2000
File Size: ~ 2MB Free to try

PowerSMS
PowerSMS is an application to send SMS messages to mobile phones over the Internet. This communication tool allows you to type out text messages and send them to a particular mobile phone.
OS: Mac OS 8.x
File Size: ~ 600K Free to try -sends only 20 messages free.

SmsComposer
"smsComposer sends different types of SMS, operator logos, picture messages, ringtones, VCards and Love sayings. For advanced user binary data can also be sent. You can set up delivery time, logging the outgoing messages into a sendjournal, phonebook is inclusive.The phonebook can be edited directly in smsComposer or in MS Access 2000."
OS: Windows 95/98/Me
File Size: ~ 2.5MB Free

Mobile Music
From the developer: "Mobile Music is a MIDI to ringtone composition software. Convert your favorite MIDI music to mobile phone ringtone. Can write your music in it. It supports many kinds of mobile phone and many models. Supports 4 kinds of language. The ringtone code for most of mobile phones is key press base code. You only press the key code into your phone. It can convert music to RTTTL code, iMelody format and EMelody format code. After you get ringtone code, you could input these code into your phone by hand or copy RTTTL code to freeware 'SMS-it' and send to your phone in SMS method. Copy iMelody / EMelody format code and send to mobile phone in infrared or EMS (Enhance Message Service). EMelody format code is only for Ericsson mobile phone."

OS: Windows (all)
File Size: ~ 1MB Free to try

eGenie
Send text messages to UK mobile phones quickly and easily.

"eGenie is a small program for Windows 95/98/NT/ME/2000 that allows you to send text messages to UK mobile phones quickly and easily via the Genie Gateway. Once you have an account with Genie, you can use the features of eGenie to send text messages (otherwise known as Short Messages or SMS') without having to start up internet explorer.

"eGenie boasts a number of useful features which are easy to use clean interface with similar look and feel to Outlook, long messages are automatically broken up into a number of text messages, address book which can import your Outlook contacts or CSV file, send one message to many different people, store you Genie username and/or password so you don't have to type it in all the time, customisable continuation markers and comprehensive help file."

OS: Windows (all)
File Size: ~ 2MB Free

SMS4Mail
SMS4Mail will check and filter your e-mail accounts and send SMS messages to your mobile phone. The program can handle up to twenty POP3 e-mail accounts and send to multiple mobile phones at the same time. You can set multiple criteria for incoming e-mails, such as the From and Subject fields. Only the e-mails that meet those criteria will be sent to your phone. You also have the option to limit the maximum number of SMS for one day to avoid spam mail
OS: Windows (all)
File Size: ~ 1.5MB Free to try

PHPmyPagers
This download is a collection of PHP pagers. It includes an SMS-Pager, an ICQ pager, and a Skyper pager. It is easy to setup, and you can adjust it to your needs. The advantage of this script is that you can easily modify it, add other pager services, and translate it to other languages.
OS: Windows 95/98/NT/2000
File Size: ~ 6K Free

Java SMS SDK
"The Java SMS SDK provides easy, high-level control of the Simplewire wireless text-messaging platform. This allows any application to easily send SMS messages, including text, ringtones, logos, and Smart Messages to cell phones and pagers on over 300 networks in 118 countries. The Java SMS SDK was designed be to be as developer-friendly as possible by hiding the intricacies of the XML format required to communicate with the Simplewire WMP (Wireless Message Protocol) servers. The Java SMS SDK makes it possible to send an SMS message off with as little as two lines of code."

OS: Windows 95/98/NT/2000 Free to try

DeskSMS
"DeskSMS is a small program to send SMS messages to a mobile phone. The only thing you need is a free MTNSMS account. Just fill in your username and password and start sending SMS messages straight from your desktop."
OS: Windows 95/98/Me/XP Free

PICQ Instant Messenger
PICQ is the first true interactive and unified instant messaging software for your Palm 7. It features a buddy list, 2-way messaging over the ICQ network, short messaging (SMS) to cellphone, and history. Future versions will have more unified messaging support for email (write and read), 2-way SMS, instant messaging to non-ICQ networks (Yahoo, AIM, MSN).
OS: Palm OS 3.x
File Size: ~ 30K Free

VMExpress
VMExpress is the stand-alone client for a new web-based instant messaging application called 'Virtual Messages'. Virtual Messages allows you to send 'invites' via SMS (cellular / mobile phones) and / or email to your friends, family, co-workers etc. and invite them to chat on line anywhere, anytime!! You're up and chatting within 30 seconds. No worries about firewalls etc. as the application is completely web-based. Features include: Buddy's, Contacts / Address book, message history and easy account maintenance. If you'd like to be able to place 'Virtual Messages' in your System Tray and have it logged on all day, you should download this. Otherwise you can simply access the Virtual Messages site at VMExpress"
OS: Windows 95/98/NT Free

SMS Blaster
ActiveX/COM-Object for SMS delivery. Freeware. Pay per SMS at wholesale conditions, no monthly fees. Text SMS, Long SMS (9 SMS), operator logos, ringtones, Picture messages, Bulk SMS. Delivery notifications for quality control. Set your own alphanummeric originator. Phone Book and Send Log. Phone number import. The Visual Basic source code is included."

.OS: Windows 95/98/NT/2000/XP Free

eZeText

With eZeText, you have a more efficient but also a very much cheaper way of keeping in touch with your collegues and friends. Getting the messages and information to its destination can average as little as a penny for each SMS message, direct from the big, beautiful keyboard of your computer to any mobile phone. "Via a computer and modem or directly via the Internet, you can have a messaging system which allows you to group 'address lists' of numbers for your teams as well as last minute reserves and also all your frequently dialled numbers. eZeText works across all the mobile networks and logs messages. There's even a built in dictionary.

Note: The Internet version of the software works globally, but the modem version only works in the UK

OS: Windows (all) Free to try

Free SMS Portals:

http://sms.aktualny.sk/

http://www.smska.cz/

http://www.sms.ac/

http://sms.gt.com.ua/

http://www.sms.de

http://www.free-sms.de/