yeah you can. at least with verizon they usually go through. worst case scenario is you have to have the account holder of the account you're porting from call our port center to confirm it.

anyway, about your issue..

if him and his mom already have verizon service, there will be no porting going on anyway. i dont have enough background on the situation to really tell, and a lot of people are easily confused about exactly what 'being out of contract' and 'eligible for an upgrade (new customer price)', 'eligible for new every two (aka up to $100 credit off the new customer price) upgrade' and so on.

if he's currently a secondary line on his dad's family share plan (aka paying 9.99 for the line per month and hence not being eligible for the 'new every two' upgrade cause it has to be $35/month or higher to qualify) he's only eligible to get the new customer price, so it wouldn't make any sense for him to have his dad cancel that line so that he can start a new one. he'd actually be paying more cause he'd have to pay the activation fee.

the solution would be what's called an assumption of liability, where he just changes the number from his dad's name to his own, and can get a new phone at the upgrade (new customer) price (same price as if he stayed on as a secondary line on dads acct) without having to pay an activation fee.

if mom also is on verizon and under dads name and he wants to add her to his plan, he could do the same process for moms number at the same time he does his, or at any other time.

i think the reason you think you'll get a deeper discount for starting a new line/phone/number under your name is because best buy's prices are cheaper for new customers than for eligible upgrades, unlike the corporate stores.. you can probably get a corporate verizon store to match best buy's new customer price for your upgrade. they'll usually do pretty much anything if you threaten to go elsewhere. if they're being gay about it use the fact that you're out of contract and can disconnect without penalty to your advantage.