That should work fine, provided your 3G signal is good enough.
The only thing you might consider is than they've just released new Slingboxes, the 350 and 500, in the US but which you can obtain via eBay to the UK.
Sooner or later they'll be officially released in the UK I would imagine, but if you wanted to be slightly more future-proof/ahead of the curve then possibly worth considering.
If you only plan to view using your phone then you're probably fine with the Pro-HD but you can get a better quality picture and (in my experience) at a lower bitrate with say the 350, if you also wanted to view on a laptop, TV screen out there etc.
Hope this helps, but in answer to your Q yeah that should work, notwithstanding Sling's tendency to break some functionality of their mobile apps from time to time (search iOS HQ issue in these forums).