Ring mobile phone to take advantage of hospitality to all comers (4,5)
I believe the answer is:
open house
'hospitality to all comers' is the definition.
(free hospitality)
'ring mobile phone to take advantage' is the wordplay.
'ring' becomes 'o' (letter resembling a ring).
'mobile' indicates an anagram.
'to take advantage' becomes 'use' (I've seen this in another clue).
'phone' anagrammed gives 'penho'.
'o'+'penho'+'use'='OPEN HOUSE'
'of' acts as a link.
(Other definitions for open house that I've seen before include "Informal party with hospitality for all comers" , "Hospitality to all comers - unlock doors?" , "Total hospitality" , "Place where all visitors are welcome" , "Unrestricted hospitality" .)