I next ring a number that's wrong (7)
I believe the answer is:
inexact
'wrong' is the definition.
(thesaurus)
'i next ring a number' is the wordplay.
'ring' is an insertion indicator.
'number' becomes 'c' (C is an example**).
'a'+'c'='ac'
'next' going around 'ac' is 'nexact'.
'i'+'nexact'='INEXACT'
'that's' is the link.
(Other definitions for inexact that I've seen before include "Imprecise - inaccurate in" , "Fuzzy - untrue" , "Not precise, like some sciences" , "Not quite accurate" , "not precisely correct" .)