I'm not 100% certain, but one might assume that North Korean cell phones can only connect to North Korean cell towers. Those cell towers could be updated to broadcast NITZ data with the new offset. Since many phones use NITZ for auto time zone selection, it will probably work - even if there's no manual +08:30 option.

And of course, some phones you can just turn off clock synchronization and just set your own local time manually.

> Date: Fri, 7 Aug 2015 10:11:35 -0700
> From: eggert@cs.ucla.edu
> To: thorsen@timeanddate.com; tz@iana.org
> Subject: Re: [tz] North Korea into +8:30 time zone
>
> Thanks for the heads-up. Less than one weeks' notice, so we need a new tz
> release very soon, which will update Uruguay too of course.
>
> I wonder what cell phone users in North Korea are going to do. The usual trick
> is to substitute some foreign city that happens to have the correct UTC offset,
> but that won't work here.
>
> Steffen Thorsen wrote:
>
> > This probably needs a new time zone abbreviation
>
> As it happens, the new zone is what zic's new %z feature was designed for, and
> if we use %z we won't need to invent a time zone abbreviation. Unfortunately we
> can't assume %z works everywhere, so the attached proposed patch does the
> abbreviation by hand; we can convert it to %z later. The patch also contains a
> change to 'Theory' to document the motivation for the %z business.
>