Since Twitter gave up on providing IM and sms access to their service, leaving most people stuck with web and api access there's been a variety of apps surfacing. Personally I use TTYtter a Perl command line app, nothing pretty, but it works for me.

Interestingly since the microblogging service identi.ca - which uses the open source tool Laconi.ca - started offering a Twitter compatible api you can now use TTYtter with identi.ca

To do so you need to edit the .ttytterrc file in your home directory so that you replace http://twitter.com/ with http://identi.ca/api for any urls, and disable polling for direct messages as identi.ca does not support these yet. The changes are as below:

url=http://identi.ca/api/statuses/friends_timeline.json
rurl=http://identi.ca/api/statuses/replies.json
uurl=http://identi.ca/api/statuses/user_timeline
wurl=http://identi.ca/api/users/show
update=http://identi.ca/api/statuses/update.json
dmurl=http://identi.ca/api/direct_messages.json
frurl=http://identi.ca/api/friendships/exists.json
dmpause=0