Yes standard and new phone cable
I use the splitter to plug into the wall, one line is my computer and the other to the landline
Yes I have use different cables and iv even tried to plug just the modem into the wall without the splitter no difference (is the another way to test the splitter)
There has been no changes in my connection (download, upload .line attuation or noise.)
There is alot hooked to the modem but when I am running tests I dissconnect all devices. Also tried nothibg plugged into it and cheaking the statics via my smart phone using wifi
About the next question, im not sure what exactly your asking about the plug but ill try. The wire coming into my house is a single wire goes to my phone socket.
I guess the phone socket it itself (the main sockets.where my splitter is plugged into..) is pretty old maybe that could be an issiue?
I agree with you completly I want to figure this out myself now and I have already learned alot
Hope this answered your questions