Yesterday's release of Skype for Linux 1.4.0.64 (Alpha) marks an important milestone for the Skype developer community: it's the first ever release of Skype for Linux where the API allows you to do things that you can't do in the UI.

The API functions can be divided into two groups — those related to features provided by the core library (e.g. managing calls and chats) and those dealing with the client user interface (e.g. browsing the contact list or opening a chat window). The UI-related functions are not yet available in this latest build, but as far as the library functions go, the UI simply provides a transport channel (or actually two — X11 messaging and D-BUS). This means that everything available in the core library is also available in the API.

Why is this important? Because Skype for Linux 1.4 is built on the same core library that powers Skype for Windows 3.2 and Skype for Mac OS X 2.6. And this, in turn, means that you can actually do things like sending SMS messages and transferring calls -- on Linux.

Here's what I've just done using the Skype X11 test client available from DevZone's sample code download area (this version requires QT3 while Skype 1.4 requires QT4 so you'll need both).

> NAME mySMStest
> PROTOCOL 7
> CREATE SMS OUTGOING phonenumber
< SMS id STATUS COMPOSING
< SMS id PRICE_PRECISION 3
< SMS id PRICE_CURRENCY EUR
< SMS id TARGET_NUMBERS phonenumber
< SMS id TARGET_STATUSES phonenumber=TARGET_ANALYZING
< SMS id TARGET_STATUSES phonenumber=TARGET_ACCEPTABLE
< SMS id PRICE 78
> SET SMS id BODY sms message text
< SMS id BODY sms message text
> ALTER SMS id SEND
< SMS id STATUS SENDING_TO_SERVER
< SMS id TARGET_STATUSES phonenumber=TARGET_DELIVERY_PENDING
< SMS id STATUS SENT_TO_SERVER
< SMS id TARGET_STATUSES phonenumber=TARGET_DELIVERY_SUCCESSFUL
< SMS id STATUS DELIVERED

Note that we will eventually incorporate SMS and other cool features into our own UI, but until then you, the developers, can make a lot of users a lot happier. And once you've got yourself up and running with developing cool Skype add-ons for Linux, the sky's the limit.

Now how long exactly will I have to wait to see the first SMS-sending add-on to Skype for Linux?