Add a fourth voice line to legacy ONE Plan All In Promo (3 voice (one free) + 2 tablet)?

I have an old ONE plan that now costs $133/month after all the recent increases ($8.33/month of the total in the screenshot below is an EIP). Includes 3 unlimited voice lines, one of which is free from an old "add a line on us" promo, and two tablet lines. All taxes/fees are included. Back before all the recent changes, I recall I was maxed out on voice lines and couldn't add any more even if I wanted to. preview.redd.it/nn3hd9969xrh1.png But now, if I try to add a new line, it seems to be telling me I can under my current legacy plan, for $25/month with the auto pay discount. I would like to add it, but not if it means screwing things up with my current plan. Is this for real? preview.redd.it/7fl6qm89bxrh1.png