First thing I have done is secure a Google Voice number and have pointed it for a month or two to my previously exisiting cell phone number.  For that month or two, I am using that to transition my clients, friends and family to the new virtual number.  Google Voice enhances the existing capabilities of your phone, regardless of which phone or carrier you have - for free. It also gives you:

One Number; Use a single number that rings you anywhere

Online voicemail; Get transcribed messages delivered to your inbox.

Once you have migrated people to your new phone number, it is time to disconnect your cell phone number.  Scary as I have had mine since 1993.  Now before you disconnect your phone you need to add another phone number for Google Voice to make a connection to.  If you are replacing a home cell phone, you may want to consider NetTalk at $30 after initial $70 investment.  For a business solution, I prefer getting a number from SKYPE at $6 per month and an unlimited calling pan for $3 per month.  Ad the apps to your smart phone and you are set.  Anywhere there is WIFI you can connect.

So now your monthly expense has gone from $70 per month to $9 per month, an 87% savings!  $8,784 over 12 years.  Now wait, this is not right for everyone.  You can't call from the golf course though the club house probably has WIFI.  You can't call from your car but in 10 states it is illegal to do so from a moving vehicle.  If your avalibility anytime is mission critical, don't even consider this.