Lifehacker breaks down the cost numbers which are valid for an individual small business person since this is how you are likely getting your contract and phones. I like having the newest fastest and shiniest phone. But I hate paying for them so I am constantly evaluating my needs with what is available. I am in a unique situation because I use Google Voice in tandem with my mobile so I actually prefer my phone number to change every several years to shake off the people and businesses that use it inappropriately.
Most small businesses would like to keep their number and the portability rules have made this simpler generally being executed within 24 hours.