Before I write this, this is ILLEGAL.
Using an amateur radio during a cell phone outage is easy and to send coded any messages is easy too.
Record a message using a book code cypher* on a tape recorder. At a designated time & frequency send your coded message at high speed. Receiving ham operator records the speedup message. Slows the message down to decypher the message using the code book.
I would also suggest sending the message using a directional type antenna like a Moxon or Yagi. With practice you can reflect your transmission against a water tower, steel building, etc too.
The reason to use a tape machine is to speed up transmission which leaves the sender less vulnerable RDF.
* Book Cypher = Two people (group) owes the same book - Title, edition, etc. The book is bought with cash in
preferred used book store. Amy how the message is a group of numbers. The number of the page, number of
paragraph, number of sentence in the paragraph and then word. So a tape recorded message would look like...
22, 2, 3, 5 - 23, 1, 1, 7- 24, 3, 1, 8, etc. Never use the same page more than once and it is best to not use
sequential pages as I just did.
Again, it is illegal to broadcast an encrypted message via a two way radio.