Tropo can't receive messages from short codes or send a message to a short code. This is because short codes are only connected with wireless carriers, and as such can only communicate with wireless numbers, and not with Tropo's programmable phone numbers.
Messages sent to your Tropo number from a short code will not arrive at your application. They won't even reach Tropo's network, so there's nothing we can do to notify you that this happened.
Messages sent from a Tropo application to a short code will not be delivered and will fail with an "Undelivered" status.