Can you telnet to the ports in question?
It wouldn't surprise me if common Windows share ports were blocked by your ISP, historically they were a common virus proliferation route when people started putting non-firewalled PCs online back in the dial-up and early DSL days.
Why the need to use Samba? Reading your AskUbuntu it seems you are using Ubuntu 14.04 on the client, presumably the Amazon instance is also running a linux variant as the topic is about Samba. You'd likely be better off using SSH / SSHFS unless there are Windows clients that need to access the share.
If you go the SSH route it would be wise to run the server SSH daemon on a non-standard port and configure it to use key authenticated login only. It's not hard to setup (as with anything it seems complicated the first time though).
Edited by GeeTee (Mon 26-May-14 05:33:11)