When I am collecting my students to enter the classroom (lab - I am a science teacher), my instructions are "Make sure you bring your phone and your laptop."
The lesson will involve some practical work (e.g. an experiment), and they will be asked to share the results on an internet forum, so that other students can also see their results and comment on them. Similarly, they are asked to write about the investigation into the forum to analyse the investigation in terms of purpose, analysis of the scientific process involved and what the results may mean. They are also asked to comment on what others have written.
The process I have just described is quite difficult without such devices - a camera is lots quicker than drawing a sketch. The collaboration reaches outside the classroom to other students.
However, the questions were:
Principal support: Whenever devices in the classroom are discussed at a policy level, myself and others using devices in a similar way state the how the devices are used, and the educational benefit of such practices. So far the school policy stands as being able to be called for or banned by each classroom teacher. Use of devices is carefully monitored in the classroom, but I try to set the bar high in terms of students completing the tasks set using their devices, limiting inappropriate activities.
Parent support: This has been difficult as it really has meant showing many students the work students produce and then describe how this is completing what would otherwise be far too difficult and time-consuming without using the devices. Most parents seem to see the benefit and are supportive.
I make no requirements about preferred platform, operating system or browser, however some rules exist in the Department's code of conduct about "appropriate use". The intention is to make whatever I am asking students to use accessible by whatever the students are using. So the majority of what I ask my students to use is accessible by any web-browser which is available on any device. The limitations are with those students using iOS (e.g. iPhones and iPads) when I have content that uses flash, or a movie format that does not work. I then need to re-write such older lessons/instructions to suit these, while still being available to others. This is usually a matter of changing it to an ordinary (html5) web-site, or using something different.
The easy way to do this is to use an appropriate system for the lesson material. My school has a Moodle server (though it is getting quite old now). Some find that Edmodo is a good platform to allow the collaboration I am describing. Google plus would be another excellent system, but it is blocked by the Department's firewall.Each of these systems have an emphasis on collaboration.
One beneficial aspect of using a forum for class discussions is that students who would normally say nothing, instead become active participants. I think they feel protected and empowered by the on-line nature of the discussion. On the other hand, loud and dominating students often feel frustrated as instead of mouthing off, they need to think about what they are writing.
Anyway, I hope these thoughts are helpful for prompting discussion. I acknowledge that this may not work in all situations.