I have an iPhone, not Android, but here's how I'm setup:
1) dynDNS entry for my server's WAN IP (for use from off-site)
2) local hostname on my SME matching the dynDNS entry (for use from the local WiFi)
3) iPhone setup using IMAP over SSL and SMTP over SSL, talking to the dynDNS name of the server
My server is in server-only mode - my dynDNS entry is updated by my router.
The objective is to get DNS setup so that 'ping <my.smeserver.org>' returns your WAN IP from off-site, but returns your LAN IP from on-site.
Additionally, I use owncloud to sync contacts and calendars between my phone, apple apps, and thunderbird.