I agree, Ronnie's voice was somewhat limited but boy was it special. Estelle had a similar singing voice but not as distinct. The Ronettes probably could have played the Copa if they wanted. Ronnie said the three of them harmonized so well [[she attributes this to the fact that they were related so they had a good blend) and you do hear it on some songs like Keep On Dancing. And then I could see them progressing towards a more soulful sophisticated sound as Eddie pointed out.