Correct me if I am wrong but my understanding is that an LTE modem configured to use frequency bands Foo, Bar and Baz might potentially be enabled to use the band Qux, if the radio allows it and is just disabled by a software configuration. I assume this is the story with said Android devices.

But no amount of tweaking can turn a non-LTE modem into LTE. The N900 does not have an LTE modem. End of story.