I have been using Ting mobile service for almost three years now. Can't say enough about how much I've loved the *big* money savings from Ting. Or the excellent Ting customer service!
For our DD's 8th grade graduation gift we are upgrading her phone to a Samsung SG3. It is a refurbished one we purchased from the Ting store.
Her current phone was a refurb from the Ting store and it has served her well these last two years.
I really like that we can buy used and save some big money - since most teens are going to abuse their phone right away anyway - *almost* new is good enough. 
So, if you are looking for a sensible grad gift, or maybe Father's Day gift, check out Ting right now and save $100 smack-a-roos! 
Details directly from Ting:
From now until 11:59pm ET on June 8, the Ting Refer a Friend program is offering you $100 to try Ting mobile phone service. If you sign up and activate a phone, I'll also receive a $50 credit.
Once you join Ting, you'll be able to refer your friends too.
That's my unique referral URL and the key to this offer. Click it or copy & paste.
You must use this to receive $100 off select phones in the Ting shop or a $100 service credit if you bring your own phone to Ting.
Speaking of which, the phone you already own will probably work with Ting. Go to the Ting compatibility checker to find out for sure.
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June 2nd, 2015 at 12:01 am 1433203260
May is the first month I had to pay anything for Ting since starting with them at the end of December.