Access Network Discovery and Selection Function (ANDSF) is still evolving and with the introduction of Hotspot 2.0 (HS 2), there is a good possibility to provide seamless roaming from Cellular to Wi-Fi, Wi-Fi to Wi-Fi and Wi-Fi to Cellular.
There is a good paper (not very recent) by Alcatel-Lucent and BT that explains these roaming scenarios and other ANDSF policies related information very well. Its embedded below: