Help Using Wi-Fi only (VoIp and Data) please

So I'm off to India for a couple of weeks and want to set my phone to only use wi-fi (for VoIP & data). I appreciate that I need to be connected to a wi-fi access point but I also know that there are many free wi-fi access points where I'm going. Is at as simple as putting it into air plane mode and then turning wi-fi back on? Has anyone done this? I'm currently on the latest Three firmware. Fritz