Surmised I said, it’s a caller (5)
I believe the answer is:
guest
'a caller' is the definition.
(someone making a visit or call)
'surmised i said' is the wordplay.
'surmised i' becomes 'gues' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'said' becomes 't' (I've seen this in other clues).
'gues'+'t'='GUEST'
'it's' is the link.
Can you help me to learn more?
(Other definitions for guest that I've seen before include "Person receiving another's hospitality" , "Hotel resident" , "Visitant" , "Caller" , "Customer of a hotel" .)