With Kylook synchronizing the address book of multiple Yahoo accounts is simple.
(*) Whether synchronizing Yahoo through the device (Kylook App required)
(*) Or with Yahoo accounts directly synchronized with Kylook web (login in www.kylook.com)
(*) Or with a combination of the last two
See this short video about syncing Yahoo with Yahoo:
* synchronize of many Yahoo accounts with one Kylook account is possible
* but one Yahoo account can be synchronized only once with Kylook