Ok - here is the setup for Telemetry that I got to work for Temperature and Voltage ONLY - I have not installed the Speed/RPM Sensor yet:

Step 1: For Temperature Sensor (heat indicator) - Traxxas Part #6521
Note - you MUST purchase this first because you can not use the Voltage sensor unless you have this Temperature Sensor - the Voltage Sensor actually plugs into this sensor.

Step 2: (Optional but recommended) - Temperature Sensor Mount - Traxxas Part #6535 - this mount is used to tightly secure the Temperature Sensor to your motor. Its optional because if you have a piece of curved plastic and a thin/long wire tie, you can make your own - but for $3.00 - its not even worth the time to make your own. Make sure you dont over tighten the wire tie, you may crush the sensor.

Step 3: For Voltage Sensor (battery indicator) - Traxxas Part #6541 - this sensor will provide you with battery voltage (or combined voltage of multiple batteries). Remember - you must purchase the Temperature Sensor as its required for connecting to your car/truck's receiver to use the Voltage Sensor.

Step 4: Make sure you plug the RED male end of cable of the Temperature Sensor into the RED female end of the Voltage Sensor - then plug the GREY cable end of the Temperature Sensor into the "V/T" slot in your Traxxas Receiver. Basically its RED to RED - GREY to "V/T" PORT in RECEIVER.

Step 5: Download the free Traxxas application from the iTunes store and install on your iPod Touch or iPhone.

Step 6: Connect TQi Docking Station to your TQi Radio - Traxxas Part #6510 (newer TQi models come with this Docking Station) Its required for connecting your iPod Touch or iPhone to your TQi Radio.

Step 7: Install iPod Touch or iPhone into TQi Docking Station on your Radio

Step 8: Turn on iPod Touch or iPhone - do NOT run the Traxxas application.

Step 9: Turn on the TQi Radio - the Traxxas application should automatically launch - if not, launch it.

Step 10: Skip or watch the Traxxas video - once video is skipped or completes, you should notice that in the upper LEFT hand corner of the application screen, the "TX" indicator icon is GREEN. If not close the Traxxas application, turn off the iPod Touch or iPhone, turn off the TQi Radio and repeat steps #7 to #10.

Step 11: Once you have confirmed the "TX" indicator is GREEN - you can now connect your battery (or batteries) and turn on your car/truck. When you do, you should notice that in the upper RIGHT hand corner of the application that the "VEH" indicator is GREEN. If not, turn your car/truck off, then turn it back on until you get the "VEH" indicator to turn GREEN.
NOTE - both indicators will look like this when GREEN:

Step 12: If you now click on the "DASHBOARD" icon - when you do, the Dashboard will start to load, and you then will see the indicators that you have installed. To test the Temperature Sensor rub the rounded end between your fingers to create heat - you should notice the temperature rise. Voltage will increase to the amount of charge you have in the battery (or batteries) connected.

So there you have it - I hope this solves the "mystery" around these Telemetry functions. Ill post an update for Speed / RPM sensor once I have the steps nailed down.