Stops supporting unlimited texts as offers (7)
I believe the answer is:
extends
'offers' is the definition.
('extend' can be a synonym of 'offer')
'stops supporting unlimited texts' is the wordplay.
'stops' becomes 'ends' ('end' can be a synonym of 'stop'**).
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'unlimited' says to take the centre (discard the edges or 'limits' of the word).
The middle of 'texts' is 'ext'.
'ends' put after 'ext' is 'EXTENDS'.
'as' acts as a link.
(Other definitions for extends that I've seen before include "holds out" , "Reaches or stretches out, say the hand of friendship" , "Stretches out over a distance" , "Makes longer" , "Widens" .)