Hi there-
I'm not aware of any studies that link cell phone use to grades, but I think that like everything, promoting behaviors in moderation is the best bet as a parent.  Cell phones have a time,place, and purpose, but concerns over the use of phones with children are important to address as well.

Have you checked out our section on Children and Cell Phones? http://www.education.com/topic/kids-cell-phones/

There is a ton of useful info on promoting responsible cell phone use for kids. This is a helpful article that considers the pros and cons of using a cell phone http://www.education.com/reference/article/Ref_Cell_Phone_Dilemma_2/

Hope this helps!
Kelly

I recently bought my 10 year old a cell phone so she could call me if she needs me. She gets excellent grades right now and so far her grades have remained the same- excellent. She is reading 3 levels above her grade. I am proud of her and I believe it is all about how and what you teach your children. If they are respectful then their should be no problem in handing them a cell phone.

Cell phones are a tool for communication. If used properly and with some parameters for a students (time, length of calls, texting), the cell phone would not prevent a student from making good grades. If the student is constantly on the phone and not attending to business, the problem is not the cell phone but behavior.

I am a father of a 16-yr old daughter.  She has been in the school system's gifted and talented program since kindergarten.  
 
My daughter has been exhausted over the last two years.  Nearly the entire time we thought it was just that there was a larger amount of homework and her demanding extra-curricular activity.  
 
Last year I caught her doing 2,500+ text messages (sent) in one month. We did not think anything of it because her grades were still high. That was 10th grade honors classes.  This year, 11 grade exposed the problem: texting addiction.
 
She looked even more tired than before, her grades were slipping. She was having a hard time focusing and communicating.  Her math scores dropped from low 90s to mid 70s.  She frequently lied to us.
 
While paying for the bill, I noticed that AT&T publishes date/time stamps of all text messages. Verizon did not do this!
 
I saw my daughter busy at Texting until 2am on game day.  Game day she wakes up at 5:30am to practice her dancing for the halftime show.  After the football game was over, she came home at 11:30pm and still test'd until 1:30am !  What a long day.   Funny thing was during last year's football championship game for Texas' largest schools, we seen our daughter next to her texting friend during a pabn shot after one of the boys scored and key interception.  Everyone in the stands were hooping and holloring. Except my daughter and her friend.  No expression, long faces, they looked as if they were zombies. I am not kidding.  And long it makes perfect sense.
 
We noticed more arguments, more drama, more dishonesty, cheating, etc.
 
Folks this is a serious problem and it can easily be hidden.  I've done a lot of research on this in the last several days and most of it is only 6 months old. It looks like most parents and people have been caught by surprise on this one!!  
 
Good luck !