Mobile broadband is unsuitable for the uses you describe. There is a technical limitation which cannot be overcome easily. The 'latency' is too high... this means that a 'ping' sent from one computer to another takes 100ms to 200ms, rather than about 30ms to 50ms which would be considered broadband in other countries. This slowness of response makes for terrible streaming of anything, .. including live football, or voip calls.
So there is a technical limitation, and mobile 3G services are called midband in other European countries for a reason,.. because it is not broadband, and cannot be substituted for broadband. It is called broadband in Ireland for a reason too... because we cannot get real broadband to people, so it is convienient for us to relabel midband as broadband, and voila, .. we now have much better broadband penetration,.. and all at the stroke of a pen.
Google just released the worlds fastest service in San Franscisco... 1Gb/s.. that's 1000 Mb/s,... or a full 700Mb movie in less than ten seconds, if downloaded at full speed.
To be fair the meteor 3G service is very fast for volume downloads (and the others can be reasonable speeds), but they are still unsuitable for online gaming, online poker, voip, or streaming.
VOIP will be specifically banned in your terms and conditions by several operators.
I suppose I should add that you may not have a choice.. I use mobile broadband and it is ok, so just go for it. Meteor currently have the fastest network.