I believe this has been suggested before, but I will bring it up again: I think PM should allow pro-rated immediate plan changes through the self-serve portal. If not all the time, then how about adopting the current new-plan exemption of being half way through your plan or less as the cut-off, and just keeping that ability all the time, and not requiring PM moderator assistance.
I personally have seen a ton of recent activations that, for whatever reason, have forgotten to add a texting option they wanted, or activated thinking they didn't need a talk option and could just use the LD add-ons (you can't!--but the system doesn't prevent you from buying them anyway), etc. I think this would eliminate a lot of manual intervention AND customer frustration, particulary for new customers, but even for existing ones whose needs can change.
I'd propose that if you have auto-pay turned on or manually top up, that the system should allow you to change the plan immediately, and charge you only the pro-rated difference (when moving to a more epxensive plan). If moving to a less expensive plan, then it should credit you the pro-rated difference into your PM account (not a refund, but a credit toward you next renewal/cycle).