AS you have had a sim only since November there 'may' be a credit check as noted in the terms and conditions (section 3 1st para)
*The Game Is On*
Yes, you will be credit checked as the device plan is a separate credit agreement.
There are no credit checks on a like for like upgrade, but as you currently haven't been checked for a device plan CCA, you will be done the first time.
Track usage, upgrade and get support with the My O2 appDownload My O2