The need to have two mobile phones is no longer a requirement. Any UC specialist (or even non-specialist) will say, 

"Why do you need a business mobile? Just link your personal mobile to your VoIP phone system and it will pick up calls and the caller won't even know that you are on your mobile as they just dialed your business land line!"

Having two mobile phones IMO is just a lazy way of staying in contact. If you like your personal iPhone, why have your business give you a Blackberry to receive calls on?