Funny ring tone - it's a gas (8)
I believe the answer is:
nitrogen
'a gas' is the definition.
(nitrogen is a kind of gas)
'funny ring tone' is the wordplay.
'funny' indicates anagramming the letters.
'ring'+'tone'='ringtone'
'ringtone' with letters rearranged gives 'NITROGEN'.
'it's' acts as a link.
(Other definitions for nitrogen that I've seen before include "It's a gas, the strange ringtone" , "Atomic number 7" , "It constitutes 78 percent of the atmosphere" , "Chief component of air" , "that's dominant in the air" .)