I tried a couple of times, with different installs, but keep ending up with the same results.
I have an Ubuntu 8.04 64 bit server installation running on ESXi, with Zimbra Community edition 6.0.6.
I'm trying to install the latest z-push version (1.3) with the zimbra.php backend, tried several svn versions.

I keep ending up with stuff like this in the debug.txt file, and no syncing happening:

Code:
05/01/10 14:42:33 [1011] Start
05/01/10 14:42:33 [1011] Z-Push version: 1.3 355
05/01/10 14:42:33 [1011] Client IP: 188.188.14.68
05/01/10 14:42:33 [1011] Client supports version 2.5
05/01/10 14:42:33 [1011] START Logon { username = myusername; domain = ; password = <hidden> }
05/01/10 14:42:33 [1011] SOAP message: <soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope">
                            <soap:Header><context xmlns="urn:zimbra"/></soap:Header>
                            <soap:Body><AuthRequest xmlns="urn:zimbraAccount">
                        <account by="name">myusername</account>
                        <password>**********</password>
                    </AuthRequest></soap:Body>
                        </soap:Envelope>
05/01/10 14:42:33 [1011] SOAP response: <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head>
<title>404 Not Found</title>
</head><body>
<h1>Not Found</h1>
<p>The requested URL /service/soap was not found on this server.</p>
<hr>
<address>Apache/2.2.8 (Ubuntu) PHP/5.2.4-2ubuntu5.10 with Suhosin-Patch Server at ---my server address---</address>
</body></html>

05/01/10 14:42:33 [1011] /var/www/z-push/backend/zimbra.php:151 Undefined index: soap:Envelope (8)
05/01/10 14:42:33 [1011] END Logon { connected = true }
05/01/10 14:42:33 [1011] START Setup { user = bram; devid = 515353555349485049485349515254; protocolversion = 2.5 }
05/01/10 14:42:33 [1011] SOAP message: <soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope">
                            <soap:Header><context xmlns="urn:zimbra">
                            <authToken></authToken>
                            <sessionId id=""></sessionId>
                        </context></soap:Header>
                            <soap:Body><GetFolderRequest xmlns="urn:zimbraMail" visible="1">
                    <folder/>
                </GetFolderRequest></soap:Body>
                        </soap:Envelope>
05/01/10 14:42:33 [1011] SOAP response: <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head>
<title>404 Not Found</title>
</head><body>
<h1>Not Found</h1>
<p>The requested URL /service/soap was not found on this server.</p>
<hr>
<address>Apache/2.2.8 (Ubuntu) PHP/5.2.4-2ubuntu5.10 with Suhosin-Patch Server at ---my server address---</address>
</body></html>

05/01/10 14:42:33 [1011] END Setup { 0 Folders Loaded }
05/01/10 14:42:33 [1011] POST cmd FolderSync denied: Retry after sending a PROVISION command
05/01/10 14:42:33 [1011] end
05/01/10 14:42:33 [1011] --------
I have tried installing a new separate virtual machine for the z-push frontend, to avoid conflicts in apache-zimbra... and pointed to the zimbra backend server, but the same issue keeps coming up.

I tried following several 'guides' on the web, like Push email, contacts and calendar with Zimbra 6 Opensource & Z-Push – ActiveSync | slashdevslashnull.com but it all turns out the same, or even worse...

Is there anyone that has a working setup on Ubuntu server?
Please let me know what these soap errors might mean, which packages need installation or configuration, and how I can resolve this problem.

Thanks for all the advice and guidance!