Blackberry Bold or iPhone?

Here’s the deal: I used to work for an authorized retailer for AT&T Wireless. As an employee, I got a discounted rate plan ($20/month for unlimited everything). I have since left the company, but am still on that rate plan wink. iPhones are not allowed on said plans because authorized retailers do not sell iPhones. I’m eligible for an upgrade and I want an iPhone, but I’ll have to switch to a regular plan which is going to cost me a minimum of $60/month. If I get a Blackberry Bold, I can keep my $20 plan. Advice?