Google Hangouts doesn't work in the default browser on Ubuntu Touch OTA10.1. It just gives a message "It appears as if you're using an old or uncommon browser that doesn't support common standards".
I also tried it with Firefox, but it claims to need a plugin, which I can of course not install.
The Ubuntu Hangups app doesn't support calls (video or voice), so it doesn't help either.
rc-proposedchannel (meaning that the fix will be available in OTA-11 in a few weeks). See https://plus.google.com/+OliverGrawert/posts/aZi13q1bcWw and https://plus.google.com/u/0/+MikeKelly87/posts/32EUgtorgWJ – Jens Grivolla May 09 '16 at 07:57ubuntu-device-flash touch --channel=ubuntu-touch/rc/bq-aquaris-pd.enfrom there (though it didn't succeed on the first attempt). Do not go into recovery mode to do it, just run it when the tablet is powered up normally (but you need to enable developer mode). – Jens Grivolla May 10 '16 at 12:31