while the other ones continue to give useful recommendations on phones, i'll make a short trip to get back to the other part of the original question: if you can obtain the invoices from your accounting, then you could calculate an average monthly consumption on voice minutes and sms messages. this would give you the best data to shop for good rates.
i have no idea on the rate differences and your monthly usage, but probably it wouldn't be so good to get a certain discount on a mobile phone which is maybe even not the very best model you can get, but your usage profile would give you a better annual voice & sms discount package with another provider.
therefore i would not only focus on which provider has got the best phone offers, but compare the voice and sms rates in combination with the offered savings on the phone purchase to get the complete picture. if you are not out for a brand-new phone, then you might be able as well to strike a good deal in mong kok with some relatively new 2nd hand phones with much better specifications, but which would be out of your 2K budget otherwise.