I try and use my phone for everything I can. Some of the apps that I
find very useful are:

1. fring (free): Works with gtalk, twitter, fb, msn etc. If you have
   one of those newfangled Nseries phones, you can use the front camera
   to make skype video calls (over WiFi).

2. Nokia Messaging Email (free beta, might change in the future): The
   native email application on the E71 is a load of crap. It’s amazing
   how they pitch it as a business phone and ship with a pathetic Email
   application. The Nokia Messaging application is pretty good, it has a
   very usable interface and supports HTML email. The only downside is
   that Nokia wants a copy of your email username and password.

3. Mail for Exchange (free) : I don’t actually use this for email,
   I’ve set it to synchronize my contacts with Google Contacts. You can
   use this for push email if you need to use it with MS Exchange.

4. Splash ID (slightly expensive, USD 29) : I have this magical
   ability of forgetting passwords and PIN codes. This is the best
   application I’ve found so far that does a good job of remembering them
   for me. The interface is slightly dated, but it works like a charm.
   Highly recommend it, as you should have different complex passwords
   for different services.

5. Truphone (free app, pay for recharges): This is similar to the
   Gizmo application for making phone calls over WiFi. It is a lifesaver
   if you need to make a lot of international phone calls. It uses WiFi
   to connect and the call is carried out using VoIP. Pretty reasonable
   rates too.

6. Putty for S60 (free, OSS): Most of you would never need/use this
   application. I use this to connect to my home computers to check on
   stuff. Also the ability to remotely reboot one’s computer is awesome.