[mkching]

Short codes are managed per country, but within the US just about every true mobile operator should have the ability to work with the same US short code. If they don't support a given code, it is because they choose not to. Part of the approval process for getting a short code is having all of the major wireless carriers sign off on your application.

If Google Fi is using SMS-enabled wireline numbers as opposed to mobile numbers then there could be additional complications.