I searched and didnt see this listed. Here is a cool application I found that works with call waiting. If you are on the phone and someone calls you, with this software (the app does have to be turned on), you can hit the # key and it will send a text message to the other person on the other line saying you are on the phone. Unfortunatley it costs $5, BUT I think it worth it.
If you’re on your cell phone and someone else tries to reach you, it’s sometimes difficult to get to the second caller before they go to voice mail. Now with
New Call Waiting (for Windows Mobile 6.0), if you can’t finish your conversation with the first caller, you just press one button on your cell phone and an instant SMS message is sent to the second caller, telling him or her you are busy right now and will call back.
The app, costs $5, does this without interrupting your conversation with the first caller. You can also personalize your messages so each caller receives a different message(up to 10 different messages).