Hi Vlad,
Glad to hear you can successfully use sample.html with your CUCM. To place a call between 2 JabberSDK-based web applications (ex: sample.html), what you basically need is listed below.
Server-side (CUCM)
[S1] 2 CUCM end users, for example userA and userB
[S2] 1 line (directory) numbers assigned to each userA and userB
[S3] 1 CSF device associated to each user, default naming convention is
ECPuser (ex: ECPuserA and ECPuser

Client-side:
[C1] 2 Windows and/or Mac computers
[C2] Install the SDK browser plugin on each machine
[C3] copy the sample application (sample.html and dependencies) locally, or host it on your web server
[C4] open sample.html in IE/Firefox/Chrome/Safari and login as userA and userB respectively
[C5] from the userA client, dial userB's number (configured at step [S2]) and click make call
As a side note, it is always helpful to have hard phones registered to the same CUCM/users for cross-testing.
Hope it helps, Thomas