Here is a collectio of adapters for different phone line connectors around the world. Those telephone connector adapters are designed to connect RJ11/12 plug cable to wall phone outlet on different countries.
Different countries use or used to use different type telephone connectors on wall outlets. Those adapters were are used convert one country specific connector to RJ11/RJ12 connector where you can plug in your modem. Click picture and zoom in if you want to see to which country they are for as each adapter is labeled with country name.