A lot of the stuff described in this document requires a Gizmo5 account, which are difficult to come by. Registrations are closed and there's no invite system, so someone has to actually give you the credentials to an account they already have to transfer it to you.<p>I have SIP set up on my Nexus One, replacing the default GSM phone functions with SIP stuff over the data band. Here's what I use:<p>1. The Android SIP client, sipdroid. <a href="http://sipdroid.org/" rel="nofollow">http://sipdroid.org/</a><p>2. An account with sipgate: <a href="http://www.sipgate.com/" rel="nofollow">http://www.sipgate.com/</a> Free signup gets you a real phone number, same calling rates as Google Voice, decent web interface. It has some features that are more powerful than Google Voice, but no transcription.<p>3. An account with pbxes: <a href="http://pbxes.org/" rel="nofollow">http://pbxes.org/</a> (Warning, their landing page has Flash with very irritating sound, yuck) pbxes acts as a programmable in-between for SIP communications, like SIP Sorcery as described in the article posted here.<p>You connect sipdroid to pbxes, which connects to sipgate:<p>Your phone (sipdroid) &#60;---&#62; pbxes.org &#60;---&#62; sipgate<p>pbxes acts as a much more powerful wrapper around sipgate. Sipgate will connect your SIP calls in and out of landlines, and pbxes gives you more powerful control over the SIP-only stuff. Even if you don't want to use the power features of pbxes, I still recommend connecting sipdroid to it instead of directly to sipgate or another provider, as pbxes has implemented a little trick that can save you a ton of battery life on your Android phone when connecting to it with sipdroid. You can read about it here: <a href="http://code.google.com/p/sipdroid/wiki/NewStandbyTechnique" rel="nofollow">http://code.google.com/p/sipdroid/wiki/NewStandbyTechnique</a><p>The hardest part of setting this up will be filling in the information for your sipgate account correctly through pbxes' web interface. It's a little clunky and unintuitive. There's a guide here: <a href="http://seethisnowreadthis.com/2009/07/11/get-sipdroid-to-work-with-any-sip-provider-on-your-android-phone/" rel="nofollow">http://seethisnowreadthis.com/2009/07/11/get-sipdroid-to-wor...</a><p>End result of all of this: Google Voice-priced calls, higher quality audio than GSM phones, same latency, same drop call rate, still have E911 service through normal GSM bands if you need it, programmable caller id, scriptable phone routing, near-perfect phone integration on Android. Ditch your voice plan.