Satellite phone, one with extremely strident ring (8)
I believe the answer is:
callisto
'satellite' is the definition.
(I've seen this before)
'phone one with extremely strident ring' is the wordplay.
'phone' becomes 'call' ('call' can be a synonym of 'phone').
'one with' becomes 'i' (I've seen this in other clues).
'extremely strident ring' becomes 'sto' (I can't justify this - if you can you should give a lot more credence to this answer).
'call'+'i'+'sto'='CALLISTO'
Can you help me to learn more?
(Other definitions for callisto that I've seen before include "moon of Jupiter" , "satellite" , "nymph revealing > heavenly body" , "Female reformed to bear" .)