It shouldn't be rocket science for them to take a reasonable share of the US smartphone market. The concept should be a pretty easy for them since they handle so many facets of the process already. They could grab the attention of the gaming and high end sector by making a phone with:
Large quality screen (or variable to keep the small pockets group happy too!)
SD slot
Removable battery
Water/shockproof standard
slide out controller (I just bought an older xperia play for $30. It's a fun device!)
Stock android. (as close as possible)
Give away PS1 games free to download
no proprietary cards, cables, or other Sony bullshit.
Reasonable cost
Free or heavy discounts for streaming Sony movies/classics
Available on all carriers. (I loathe AT&T, but I'd almost consider switching from Verizon to have access to all phones)
Most consumers won't give a crap about most of these things, but if they can get the gamers and enthusiasts, it'll create a great buzz. It would certainly open the door for attention to non-gaming models. Best of all, this is almost all existing resources and hardware, and not much custom software, which the consumer DOESN'T WANT ANYWAY.
They should be able to use their brand and resources as a weapon. It could create a great amount of goodwill. Just stop with the awful formats and trying to pull every dollar out of a customer with "me too, but worse" products and services.