I don't think landlines will be obsolete anytime soon. They have their advantages over mobile phones.
Traditional phones are cheaper to replace than mobile phones.
Signal interference is less of an issue (unless you happen to be carrying a portable cell tower with you everywhere you go!).
It's much more difficult for hackers to compromise the traditional phone line. This is vital for businesses.
Until we can take care of some of these issues, landlines won't be going anywhere.