In my experience I didn’t see a fixed line calling another fixed with a wrong CLI. because the message is carried in IAM message in SS7 or SETUP message in the PRI protocol. The problem is with the mobile network where most of the confussion comes from, call forwarding can greately effects the CLI. Sometimes, a loop of call forwarding is created and passing through dozens of trunks, some trunks have a parameter which eats away the first two digit that might be the area code, so the called can see the calling number without the area code. This is exactly what happened to a network, have you ever seen a CLI 22 OR 1. This can be avoided by a parameter in the HLR which is MAXIMUM call forwarding times. Beside, if there is a problem with the CALLING LINE IDENTIFICATION PRESENTATION(CLOP)it can also bring this problem. The function of this CLOP is to indentify to whom you are actually connecting. For example subscriber A dails subscriber B, and B is forwarded to C. After C answers the call from A the displaying number in A mobile phone is changed to subscriber C. So you can identify that B has forwarded you to C.
One day, one of my co-works was having a relationship with a girl and suddenly they broke up, and he stopped answering from her number, another guy also knew about the story, he took the mobile phone from my co-worker and he saved her number 746466 with the name 789948. That means everytime she tries to call her boyfriend number,this number 789948 displays on his phone. which he actually don’t know about this number. After he answers the call he turned back with a red face saying “its her what shall I do, I don’t wanna talk to her, by the way what happen to the mobile network. Because if he dail both numbers 746466 and 789948 the same lady will answer, I was responsible for the NSS part of our network so I checked if both numbers have some Call forwarding number activated, but there was no services. I got confused but after a long thinking I called my co-worker and told him to bring me his mobile phone and I checked the contacts menu and I found out that trick.