Usually, the two outside pins are the line but in the UK it's the two middle ones for some reason. Please edit your profile so we can tell where you are.
The telephone connections vary country by country, there is no standard. Usually only two wires are used and it doesn't matter which way around they connect. If you can open an existing phone socket you should be able to see which ones are used in your locality.
I have worked on telephone systems from all over the World and I have never seen a phone that doesn't have a bridge rectifier across it's wires. It is there specifically so the wires can be reversed without causing a problem. In some countries the phone lines are not even color coded so it's impossible to know which way to connect the phone unless you use a voltmeter to check.