Telecommunication is the assisted transmission of signals over a distance for the purpose of communication. I am focusing on the way things work in the UK. The traditional telephone is the obvious example of a telecoms device. Later you could use a modem to connect a computer to the Internet over the phone network. Now you can get an Internet connection and then use it to make phone calls using VoIP.
A "land line" can be frequency domain multiplexed with the low frequencies being used for traditional phone communication and the high frequencies carrying the data (eg PPP over ATM) necessary to connect a computer to the Internet - this is "Broadband" or "ADSL". Cable companies such as NTL have laid their own cables to supply phone, television and Internet to many residential areas.
Mobile phones are taking over from landlines to some extent. They can be used to make phone calls, send and receive SMS messages (texts) and (with some sort of data plan) connect a computer to the Internet.
www.zenatode.org.uk Ian Gregory 2010