New ringtone is a gas! (8)
I believe the answer is:
nitrogen
'a gas' is the definition.
(nitrogen is a kind of gas)
'new ringtone' is the wordplay.
'new' is an anagram indicator.
'ringtone' is an anagram of 'NITROGEN'.
'is' acts as a link.
(Other definitions for nitrogen that I've seen before include "It comprises about four-fifths of the atmosphere" , "Much of what we take in" , "Chief component of air" , "Gaseous element" , "creates much atmosphere" .)