I have pushing the limits of my Motorola e680i smartphone that my wife bought in China back in 2004. The e680i is notable as it is one of the first generation of Linux-based phones that allow you to hack the OS. Other than hacking the phone to use internet connection sharing via a Bluetooth gateway on my home network, I haven’t done much hacking. I thought I would take a look around for some FREE, useful Symbian-based mobile apps. Here are my top:

OperaMini
What sold me on this slick mobile web-browser was it’s ability to render webpages in either WAP-style text only or full layout HTML. Lots of configurable features have made this a permanent feature on my phone, but by far the best feature was the way Opera-Mini renders the Netvibes mobile portal. All my POP email, social networks, and top RSS feeds render very quickly and also allow me to one stop post to most of my accounts. This is pure gold for me and saves me some of the per-packet gouging I am forced to endure from my mobile provider.

eMoze
I am not a Blackberry fan and refuse to buy a locked phone (yes, I’m looking at you Rogers), but would really like to sync my Outlook Calendar and have access to my OWA Exchange email on the go on my linuxphone. eMoze is a FREE Java app that will allow you access to your Exchange account and sync your mail and calendar. It also allows you to connect to any POP or IMAP email account as well as Gmail. Like OperaMini, you can block images and filter message sizes to keep the mobile bandwidth hounds at bay.
Not an extensive list, but everything I use my mobile for through work and play is covered by these two apps.