Star is, as usual, spot on. No signed contract, no phone. Make her sign it in front of a notary so that she can NEVER accuse you of forging it or changing the terms.
You are to have access to ALL texts/emails/etc... This is so that if she is dealing drugs (I think I remember you saying something about that on another post - sorry if it wasn't you), you can see messages about it (even if theya re in code you can often either look up current meanings for the words (like molly for ecstasy, etc...) or go with your instincts if they say she is up to something.
ANY use of the phone for anything related to drugs (selling, using, being around users, etc...), casual sex, prostitution, drinking, smoking, or anything esle that is illegal means you turn off the phone permanently for anything other than calling you or husband).
In addition to the ten dollars, if the minutes/texts/internet used goes over the amt in the contract, difficult child pays it ALL before the phone is turned on again (IF it is turned on). Even if "her" minutes are not over the limit, if they push "your" minutes over the limit she has to pay. WHY? because with-o her using the phone you would not every go over your minutes.
Give her a set # of minutes each month. If seh watns more she pays at the per minute rate in the contract with the phone company. If you and husband haven't used your share of the minutes and it means hers do not go over on your bill, so what? She still used more than her set amount and still has to pay for them at the higher rate. If there is no higher rate in your contract, put a charge of 10-30 cents per minute in the contract she signs with you.
Make her pay for the phone insurance AND anyhting done on the phone if she loses it. Once she reports it and it is cut off, she must pay for the activity done while it was stolen before she gets any more minutes, etc...
She must replace the phone on her own if it is lost, stolen or damaged. She STILL has to pay the monthly amount even if she doesn't have a cell phone. Cell phone companies don't really care if you have the phone or if you lost it or it was stolen. You entered into a contract to pay $x per month for the minutes, etc... and if you don't use them it isn't their fault and they are NOT letting you out of the contract, charging you less or giving you a free phone. There is NO reason that your difficult child should get different rules than this.
SHE must pay for notarizing both her signature and yours/husband's on the contract. This contract is for HER benefit - NOT yours.
If she harrasses anyone and gets into legal trouble for it, she loses the phone. If she gets into legal trouble other than a very minor traffic accident that does NOT involve texting, drugs, alcohol, or hurting anyone, the phone goes.
If she does not return your calls and husband's calls in a polite manner within 10-15 minutes of you calling, the phone is turned off.
If she commits to send $$ to a charity by texting something, she must pay it before she gets more minutes - and she still has to pay the monthly amt on time every month in addition to the $$ she pledged via text. If she buys an app or something for her phone, or a ringtone, it must be paid for BEFORE she buys it. buys it before she pays you for it? Phone is turned off and she still must pay for the app and the monthly fees.
If you, husband, or another adult hears her talking about something you find disgusting (unless you are in a home that SHE is paying for - in which case she can find her own phone anyway), like hooking up, using drugs or alcohol, gang stuff, criminal activity, etc... the phone goes off.
The contract should also say, VERY CLEARLY, that she does NOT get warnings or "second" chances of any kind. The phone will just be turned off without you or husband saying a single word to her. NO negotiations, manipulation or justification. If she is setting up a drug sting with the cops or DEA or Homeland Security she would be given a different cell phone and phone # - she would NOT be using yours. Ditto other outlandish ways to show she wasn't doing what you thought - seh was trying to "help" someone because she is a "good friend'.
Be very very sure to NOT give her another chance if you think she is dealing or selling drugs. If she is caught she can put blame on you even if you were unaware of her actions. Then you can have your assets forfeited to the govt because you "helped' her sell drugs. Even though you didn't really help. THey can claim that providing a phone for her when you knew/saw/suspected involvement with drugs means that you were supporting her actions. It isn't as rare as you might think.