Support multiple carriers sharing the same SMS e-mail gateway

SMS Framework has an array of SMS e-mail gateways keyed on the gateway domain.

However, at least in the US, there are MVNOs (mobile virtual network operators) which share an SMS e-mail gateway.

For example, Straight Talk shares its SMS e-mail gateway vtext.com with Verizon, but has its own MMS e-mail gateway: mypixmessages.com. Thus sites that are sending/receiving MMS via e-mail (in addition to SMS) must regard Straight Talk as a carrier distinct from Verizon.

I'd suggest assigning some other alphanumeric key for each mobile carrier, and building out an array with metadata for each carrier: human-readable name, SMS email gateway, MMS email gateway, country code, etc.