单项选择题

In the last few years our communications network has been growing at a very fast pace. The old fixed-line telephone has been replaced by mobile phones, Short Message Service (SMS), e-mail and instant messaging (IM). And there are other new ways of communicating related to the Internet, such as blogs.
A recent study in Switzerland shows the different roles that communication methods can play. Stefana Broadbent is a scientist at Swisscom, Switzerland’s largest telecoms company. She studied several hundred consumers and their reactions to telecommunications. She found people were very good at choosing the best technology for each situation.
"IM is used to tell you I miss you; e-mail is to organize our dinner; voice mail is to say, I’m late; and SMS to continue our talk on the way, "says Broadbent, joking a little.
Landline phones are an open channel. That means people use them to talk about nonprivate things. That’s because other family members or colleagues have access to the phone.

What does landline phone refer to（）

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