sendSMS 0.3.0 (by Erlend Aakre)
sendSMS is a small desktop application for sending SMS messages.

sendSMS 0.3.0 (by Erlend Aakre)
sendSMS is a small desktop application for sending SMS messages.

SMS Client 1.1 (by Team Aspirine)
SMS client is a simple client for Clickatell™ SMS Services.

MailTicker X 0.5.2 (by Sebastian Krauss)
MailTicker is a small application that sits in your menu bar and checks POP3 accounts in regular intervals for new messages.

SMS Yahoo! 1.2 (by Sanity Software)
The SMS widget for Yahoo! (aka Konfabulator) allows you to send text messages to mobile phones.

HighVIP 2.5.0 (by HighVIP.com)
HighVIP allows users to send and receive secure and anonymous email, chat and exchange secure instant messages, and create secure message boards.

Mailing List Account (Entourage) 1.0 (by Paul Berkowitz)
Do you find that you are constantly getting messages bounced back to you from mailing lists to which you are subscribed from a particular non-default account, because you keep forgetting to set the correct account from new mail messages and send from the default account to which the new message wind

Prattle 0.3 (by Bing-Chang Lai)
Prattle allows you to control Adium from your mobile phone.

smsZap 1.0.1 (by Bayham Systems Ltd)
Send SMS (Short Message System) text messages from your Mac to mobile phones, without needing to connect or sync your own phone to your Mac.

Request Receipt 1.0 (by Paulo Jorge Gois)
I think that in the present Microsoft Entourage can only be configured to request receipts for messages you create if you add an additional header to the account from which you are sending the massage.

2sms.com Widget 1.0 (by Charlie Boisseau)
2sms Widget allows you to send text messages to mobile phones via the UK SMS-provider 2sms.

Skype 2.0.0.6 (by Skype Technologies S.A.)
Skype is the next phenomenon from the people who brought you KaZaA.

Ovolab Phlink 3.1 (by Ovolab)
Ovolab Phlink, combined with the Ovolab Telephone Adapter, can answer telephone calls and identify the caller using Caller ID and Apple's Address Book.

BluePhoneElite 1.1 (by Reel Intelligence)
BluePhoneElite extends the calling features of your cell phone to OS X with a simple yet powerful interface.

Send SMS 1.7 (by Alco Blom Software)
How do you send an SMS? Are you using the T9 input method? Are you also wondering why you are using these small keys with numbers on it to enter text while you have your Mac keyboard in front of you?
Then the Send SMS widget is for you.

Hold On 0.6 (by Wooden Brain Concepts)
HoldOn lets you use your build-in modem as a speaker phone to listen to the line while on Hold.