How can I leave a voicemail without calling on the iPhone?
Back in the old days it was possible to call your voice mail box, choose the right option, and enter someone's phone number to record a voicemail message without calling them directly. The iPhone has changed all of that with visual voicemail. Although this option is no longer available, you can still leave somebody a voicemail without ringing their phone.
You can use Slydial, which can be found on the web at www.slydial.com. The service is free with advertising or can be purchased ad-free with a monthly subscription or per-use fee.
Slydial also has an iPhone app to streamline the process of sending voicemails.
Be warned: some users have reported that Slydial actually does not go straight to voicemail, but will register a missed call as well.