I see. I thought you were saying you had a $5 trade in CREDIT. For this they'd calculate the monthly cost of the phone and credit you the difference to make the net cost $5. This may be a different value for everyone depending on local sales tax.
Example: the phone ends up costing $17.95 per month.
You see a bill credit of $-12.95 every month
Phone still comes up as $17.95 but net cost to you is $5.
They also tend to apply credits a few days before a new bill hits. My bill hits in the 10th of the month. Around the 5-7th my bill reads $-21 for the three phone credit promo.
I'll add that any credits you're supposed to get, make sure you have a clear understanding walking outbthendoornwhat your monthly bill will be. My credits and a lot of other things were messed up for about four months. They fixed it but it took a lot of diligence on my part.