Carriers will offer better deals on the phones though if you're planning to stick with them.
I'm looking at a $1000 phone that ATT will give me for 2.99/month for 2 years. That's over 85% off on the phone. The trick is they give it to you by actually charging like $42/month, but then giving a $39 credit every bill for 2 years, so you have to pay the difference on the $1,000 phone if you jump carriers.
But since they're the only carrier that works at my office, and this is gonna be a work phone (my company pays me a monthly stipend for it), I can live with that.