Build a free VOIP for your domain.

A full article would be made available at http://www.debilloez.net/.
But in the mean time for the most motivated, here find your own informations or materials.

1. Buy VOIP credit to call land line:
I used: http://www.voipstunt.com/

2. Register the SRV record in your public DNS
More info: http://www.voip-info.org/wiki-DNS+SRV

3. Found the hosting SIP Server for free ... I provide the GOOD url ;-)
Regiter for you domain here :http://serweb.iptel.org/user/reg/reg_domain_1.php?phplib_Session=ad11955f369a073c2905e6f6d0bd0ae8
Take care to not simply register for an account but well for a domain

An alternative is to host and publish your own VOIP server (Asterix, 3CX, ...)

4. Obtain a SoftPhone and register with your accound.
By the step 3 you get a way to register by using ie toto@mydomain.com
So other SIP phone can call you by your own e-mail address !

PC Softphone : http://www.counterpath.com/
Windows Mobile : check http://www.xda-developers.com/ but many non"natif" exist.