I second what Lobo said on the original PR:
Adding the country code to the civicrm_country seems to be a logical step. I suspect that DB is available on the web.
Note that there is a column for idd_prefix in the civicrm_country table already. It is not populated, but you will not need to create the column
I just came across the problem that Sarah is fixing here - and I'm glad to find this patch, which I'll be testing momentarily.
That said, two things. First - this extension is no longer part of CiviCRM core, so I don't know that this patch make sense. Second - Sarah's suggestion that the country code be a field in civicrm_country seems quite sensible, if indeed it's a one-to-one correlation.
Can a core team member comment on how they feel about that? If so, I'd put it on my list of "patches I can do one of these days".