On the call settings page, you have the option to configure your Caller ID.
The Basic Caller ID is what is shown in the call log. If this is not turned on then in the call log it will show "Not Provided." In the US, basic Caller ID will include the name, phone number, and location that the number is registered in. In other countries, Basic Caller ID will include just the phone number and location of the caller.
The second option is to enable Enhanced Caller ID. This will look up the name, billing address, gender, and email address for many of your callers. You will be charged the first time caller dials in and only if there's a match. Cost is dependent upon the plan that you are on.
The third option, "Show tracking number as Caller ID," is what the person answering the phone will see. Selecting this option will show the receiving party the tracking number as the Caller ID instead of the caller's information. This is useful if you have numbers forwarding to your cell phone, so you can see the tracking number (and therefore know the source) of the person calling. If you are forwarding a toll-free tracking number to another toll-free receiving number, it is not recommended to use this feature, as certain toll-free carriers will not accept a call from another toll-free number.