Ah, OK, so you've found the big cross-connect punchdown block for your area! If this is attached to the side of an apartment building or block of condos or something, this is where /everyone's/ telephone line comes in.
Basically, the telco pulls in a large number of pairs to these boxes and punches them down on one side of the white vertical blocks you see. The blocks have metal teeth that stick up, which are 66-type punchdown connectors. You press a wire into the split in the tooth with a special tool and it splits the insulation and makes a connection. The 66-type blocks come in two major types: the kind where all of the teeth in a horizontal row are connected together, and the kind where half of each vertical row is connected and requires a 66-type bonding jumper to connect the two halves.
Depending on the utilization in the box, most of the telco pairs may not be in service. The ones that are will have another pair punched down near them (see above, depends on the punchdown block's structure). You can clip on to two of the metal teeth for tip and ring. Study up on the color coding for 25- and 50-pair cable!