Last year, the company Apple uses for financing ran hard credit checks on most folks.I thought I saw somewhere on the AT&T site that the NEXT plan would now require a credit check. I'll see if I can find that again.
This is what I saw:
AT&T Next®/AT&T Next Every YearSM: For smartphones only. Divides retail price into monthly installments. Requires 0% APR monthly installment agreement and eligible service. Tax due at sale. $0 down requires well-qualified credit or 30% down-payment option available.
If you have an ATT account, I think they only do soft credit checks for Next (or adding lines).