PhonerLite is a fairly popular free sip client. But from the first time it's not easy to understand it, the reason for this is not an obvious way to transfer calls and select recording / playback devices. Many do not understand how to do it, from which the soft-background reject.
Five not obvious chips:
1) Conditional call transfer.
First, we will call two interlocutors, after which we take and drag (drop) the second to the first.

2) Unconditional call transfer.
We establish a connection with one subscriber, enter the number or SIP address of the second subscriber, after which we take and throw an active call to the previously dialed number in the window.

3) Select recording / playback devices.
Click the right button on the microphone or speaker.

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4) Getting subscriber information from your CRM via http.
In the telephone directory, we indicate to the contact a comment in the form of a link, for example "
http://ya.ru ".
After the call, we automatically open a tab in the soft background with this page (uses IE).

5) Local conversation recording.
During a call on the active session, right-click.
In the call history there will be a link to the file.

Other advantages:
- reliability (in my opinion, this is the most reliable soft-background, including among the paid ones)
- TLS SRTP ZRTP encryption
- alarm on incoming call to any sound device
- settings profiles to switch between multiple operators
- OPUS codec support
- local conference (maximum number of participants did not check)
- phone book in the form of a csv-file (in the program folder)
- google contacts
- Support for some USB phones and wireless headsets plantronics, jabra
- the ability to call SIP links in the browser and not only
- auto talk volume leveling function (normalization)
- Built-in echo canceller (do not use with system)
- support for many languages, including Russian
- possibility of using without SIP server
- availability debug log
- realtime packet statistics
- constant updates
- there is a portable version
Disadvantages:
- the inability to limit the number of simultaneous incoming calls
- closed source
- icons