I attended a TeleNav event a few months ago (still owe you all a write up of that) and one of the upcoming services we were shown is OnMyWay that was released today for the iOS and Android platforms for free. It has been available for BlackBerry devices since early this year and has been downloaded by tens of thousands of BB owners.
As stated by TeleNav:
OnMyWay is a simple-to-use notification application that automatically alerts a pre-determined person or group of people of the sender’s trip status and estimated time of arrival (ETA). Drivers can quickly set an OnMyWay notification prior to getting on the road and the application will automatically send travel time updates based on location to designated contacts via text and/or e-mail.
You need to enter your destination and schedule details (appointment time) and then select the people you want to notify (it integrates with your address book) with a personal message if you like. Just to be clear here, you do not need to be using TeleNav's GPS navigation solutions to use this utility, it is a stand alone GPS location-based notification system that just uses your current location and the destination you enter to perform the calculations.
Your recipient(s) will receive notices when you leave and an ETA, based on your GPS location, and then up to three additional status messages may be sent based on your preferences. OnMyWay does not share your specific location in the notifications.
I installed OnMyWay on my HTC EVO 4G, found now in the Android Market, and plan to test it out soon. You can also find it now in the iTunes App Store.