BBM is great, but most people I know with blackberries dont even use it. Iphones have imessage. BBM has a separate "pin" number, much like nextel phones had a beep beep number. With imessage, it goes by your phone number so whenever you text someone with an iphone its automatically an imessage. Much appreciated because you get the delivery /read reciepts, also when they are typing.
I gave up waiting on the blackberry z10 when the Iphone 5 came out and I needed to switch my carrier plan due to going over on minutes. Blackberry will get the job done, dont let people say its outdated. It will do what you need and give little problems. Much more efficient than an iphone, but ios is huge and has apps for everything. Blackberry has utilities, which ios has to be jailbroken to even use. Blackberry lacks games, and "an app for everything." My playbook has zero apps, but I can do anything via the web browser since it has a full webkit. Thats the main reason I chose it over an ipad, since the ipad has a limited internet. Not sure what internet capabilities the z10 has, but if its like the playbook, its superior to ios safari.
If your looking to sell your phone to switch carriers, you will most likely get considerably more via ebay, craigslist, private sale, or a site like gazelle, amazon instant purchase, bestbuy instant purchase, etc.