If you were wondering about the correct format of US numbers then this might come in handy. In short: The proper way to send CallerID number is 10 digit (from NANPA numbers), no preceding 1 or plus sign (+) as this is handled by the provider to the end user if at all.

How many numbers to send?
First of all, if you are sending a CLID inside the US (Home NPA Local Calls) you should not send more than 10 digits (do not include the ‘1’) or your call might be considered “Home NPA Toll Calls” or “Foreign NPA Toll Calls” and some providers might block you.

What does the plus (+) sign means?
When you are making a call, the plus sign (+) is an abbreviation that  means “this is an international call” and instructs your cellphone, for example, to replace “+” with whatever is the international dialing code for the location where it’s currently located (for example, in USA it would be replaced by ‘011’). So, if you are sending a CLID, do not send it either.

If you receive a call and the CLID have the plus sign, it means that it is an overseas call.

Finally, the providers do not send 1 on the PSTN. The fact that you see a + in your CallerID is often because your mobile phone automatically fills it in, as well as the 1 (when the call is US).