&gt; I would really love to hear a telecom engineer explain why the true origin info isn&#x27;t accessible to the called person. A telephone call is a two-way connection -- the path in both directions must be known otherwise you won&#x27;t have a two-way conversation.<p>Telephone isn&#x27;t really like IP routing. If D wants to call P, the connection might get set up like this:<p><pre><code>    D -&gt; K -&gt; H -&gt; V -&gt; P
</code></pre>
P only knows that they are speaking to V, and D only knows that they&#x27;re speaking to K.<p>See what happens is D sends a message called &quot;Call Request&quot;. This creates a channel id (D,C1) between D-&gt;K. K will then create it&#x27;s own &quot;Call Request&quot; with it&#x27;s own channel id (H,C2) which tells H to bill K for this call. Only K will know both the channels C1 and C2 and will bridge them internally. When H makes a &quot;Call Request&quot; to V, it has it&#x27;s own billing arrangement with V and they agree to simply count calls, so H doesn&#x27;t actually forward anything except the channel id (nil,C3). V gets away with this because the wire is clearly marked with &quot;K TELEPHONE INC&quot;. Eventually P gets an &quot;Incoming Call&quot; message with it&#x27;s channel id (P,C4), and can accept the call or reject it. If he accepts it, then each party will send &quot;Accept Call&quot; messages back down the chain.<p>These channel ids are used to actually carry the phone call (or data packets, or whatever).<p>&quot;Caller ID&quot; isn&#x27;t the &quot;source of the message&quot;, just some data transmitted along with the ringing sound, and as you can see the circuit doesn&#x27;t have a globally unique identifier. If someone doesn&#x27;t transmit who to bill, then nobody will get billed for that call (and maybe nobody will be!) but V doesn&#x27;t want to send bills for this call <i>all over the country</i> so V only sends bills to a few carriers and its own customers.<p>All the bills have the &quot;correct calling numbers on them&quot; because of some extra billing data that&#x27;s included in the call. This billing data might be omitted (the bill says &quot;NUMBER BLOCKED&quot;), and it clearly isn&#x27;t required to establish the call. People can ask their phone company to ignore calls that have a blocked number.<p>Phone companies used to trust each other not to spoof this information, and now that calls from certain numbers aren&#x27;t usually billed differently than from any other numbers, this doesn&#x27;t cause a problem with billing -- only with people who seek to use &quot;making a call from&quot; an authentication method.