You could take both those iPhone4's over to www.PagePlusCellular.com (PP) if they are both VZ handsets.
You would continue to use 100% VZ towers and the girls will really see no change in their usage experience. You also save by not having to buy handsets.
Mom: aka "the talker"
PP plan of $29.99 will give her 1200 minutes (cutting it close if she used 1168)
3000 text is more than she will ever use.
500 mb data may not be enough, but, if you want savings, then push them to use wifi as much as possible and cut back on data hog functions.
For just $10 more, she can have unlimited talk.
Daughter: aka "the texter"
She will need the $39.99 Unlimited talk and text plan to get the texting she "needs".
I buy my airtime through www.pincheap.com at a discount and the $39.99 plan has a total cost of $36.95
The $29.99 plan is $27.70
Both at $36.95 would = $73.90
Mom at $27.70 and daughter at $36.95 = $64.65
Both versions are more than the $50, combined you had hoped for.
What is your total expense currently?
Of course, in this version both of the girls would be on smartphones.
In this plan, the princess would get her first smartphone and this could open you to data abuse, but, these PP plans are limited to 500gb. Encourage her to use wifi. She can see her usage at any time. If she hits the data wall, the data stops flowing until the renew date. She will still have talk and text capability and she will still have the ability to use wifi.
You will get no surprise bill (like you will with contract service.)
As a parent, you will have the ability to let the service run out on her handset. If on contract, you will still pay for the service even if you are grounding her from the phone.
If you find that she is good with the gift of phone you have given her then up the service to the $55 ($50.88.) This could be done some months and not other months. You are free to choose.
PP shows these two retailers near you:
Class Cellular
1115 W University Ave
Gainesville, FL
Prepaid Wireless Connection
404 S Main St
Gainesville, FL 32601-6722 Phone: (904) 364-3849
They can port over your current phone number so the girls will still have the same phone numbers.
All of this assumes that your current contractual term with VZ has been met and therefore you will have no early termination fee. Check with VZ to be sure of this. If you plan to port you will need your VZ account number as well as your account PIN code.