[ossiblue]

As you speculate, it is likely a phone or cable company line. You should be able to tell which by looking at how the connections are made between the overhead lines and the houses they feed. If it is a coax connection, it is a cable company and you should be able to readily identify them as they probably have a monopoly in service to your area.

If it is a phone line, again look at how it is connected at a house, if possible, that may be a bit difficult but if you don't have a land line, someone in your neighborhood may and you could ask them.