This paper presents our solution to supporting runtime migration of Web application interfaces among devices offering different interaction modalities, in particular graphic to vocal platform migration and vice versa. Migrating between platforms implies keeping track of the user interactions in order to retrieve the runtime state of the interface and maintaining interaction continuity on the target device. The system can serve user-issued migration requests containing the identifier of the selected target device, and can also automatically start the migration procedure when environment conditions require it. In automatic migration the target platform has to be automatically selected as well. To this aim, we consider devices belonging to a restricted environment and have defined selection rules in order to identify the most suitable available target for the ongoing migration.