A little context would be helpful.

Anonymous free from most land lines.. what does this mean ?

Free from the most telephone lines (for transmission) made of the metal wire or fiber optic cable. It's possible that they may be, otherwise, using mobile (wireless) lines which use radio waves for transmission.

If this is referring to a telephone call or number, land-lines are traditional phone lines of cable in contrast to mobile telephones.

More context would be helpful, but it is probably a statement that there is no charge for the call if calling from a land-line. The person making the statement most likely cannot make the same claim about calling from one's mobile phone since each carrier