There are two different scenarios the MMS message will be sent as an SMS with a URL link.
1. When you attempt to send an MMS message, if the recipient is on a carrier that does not support MMS, Wire2Air will send the message as an SMS with a URL linking to your media. This includes both international carriers as well as unsupported carriers in the US and Canada.
2. MMS message rejected by the carrier due to any reason, we convert an MMS message to an SMS and re-route it.