I'm curious to know, is it possible to run a server on a phone and use the phone's mobile connection as the external IP? I've seen many servers (web, ftp, etc) for android phones, but many of these say that it will host the server over wifi. I'm wondering if these types of servers can use the mobile connection to host their files?
AFAIK, the phone has an IP address and no firewall.
EDIT: This is not a discussion whether it is prudent to use the cellular connection, just whether it is possible.
While it is technically possible to host a server on a phone, it is unlikely to be usable without a special arrangement from your service provider (teleco). The phone sits with one or more firewalls and NAT devices between it and the internet. For most cell companies, these are configured to block incoming connections to the phone and so your server is not usable. For some companies, special arrangements can be made to allow such access. These arrangements are more often made with secure sub-networks than the open internet. Note that once incoming connections are allowed, you have no control over bandwidth use as people can, and will, just hammer your IP address.
Ps. Note, I say "most" above as I have seen, very rarely, telecos that allow incoming connections. They usually fix that fairly quickly.