You're fortunate to have your Mom who is able to help you with these things Christine.
I know my Mom was a huge asset to my business. She made my face cradle and bolster covers, did my massage laundry and helped me with my bookkeeping, though she didn't answer my phones... her help was invaluable otherwise!
My tax preparer commented on how the last 2 years I've come in fairly "last minute"... and I told her, "Hey, my mom died, I'm working with a handicap here... cut me some slack! At least I'm getting in by the 15th and not filing an extention!" LOL
I would think that the 2nd phone being bought entirely for your business would be deductible... plus if you have certain plans, you can get free mobile to mobile calls which can be great as far as not using up your minutes.
The only trouble I see is that for those with parents who live in other states, it may only work for you to call them... and not them to call you. As I believe cell phones are determined on your home calling area.
My nephew's been through several cell phone companies trying to get one that Truly offers a nationwide service... ah the joys of being a "traveling" salesman! LOL