Is landline phone hacking possible?

I will echo what daba said, and add this; it is possible to "hack" into someones phone line, and you do not need to be neighbors. All you need is access to a trunk line. This access could be the demarc (demarcation point) on the building, a junction on a pole near the street or an access panel at the enterence of the subdivision. All you need is any active phone line. After you find an active line, you can bridge (half-tap) to an inactive line and now both are active on the same number (or port in the central office). This is a very serious matter. It is a federal offence to do this. It is also a state offence called "theft of service". You need to contact your state attorney general office and tell them what is happening. They will then have the local telco to investigate. The telco will search the phone line and hardware for half-taps and evidence of illegal access.  more