If it is restricted to incoming messages then there could be two carriers in the path - the carrier of the originator and Fido.
Have you tried to track which messages are delayed?:
- are all messages delayed?
- are the delayed messages only from one other carrier or from variety of carriers?
- are Fido to Fido messages delayed?
- is it only pure text messages or are they perhaps email to text messages that travel through a gateway?
- does the timestamp on the incoming message on your phone show the origination time, or the actual arrival time? If arrival time, then do you have proof you can show to Fido that they're not arriving on time.
It could well be the system is based on the same chat system that the Fido Chat customer service support uses. It seems they average about three to four minutes per response and when I ask them, most of them tell me that the messages arrive that slowly. (of course I am kidding here, they are handling 5 customers at once and chat is not based on SMS technology).
