I recently purchased an iphone 7 from this deal on Groupon: Apple iPhone 7/7 Plus/8/8 Plus/X (GSM Unlocked) (Refurbished A-Grade), Order # [protected] The phone initially connected to my AT&T network, but after a few hours it started losing service and finally said "No Service" and under Cellular in Settings it said "error" and told me I have to update to use cellular data..even though I already updated to iOs 12 when I hooked the phone up to my itunes to restore from my last backup when first starting up the phone. Eventually service came back when I turned my phone off and on, but once again I am having the same problem with Cellular Error.