You mention the number of calls in queue, but not any information regarding the number of agents or calls ringing ... All Calls Count when determining the reason for system load. Also, there is no "queue", there are ingroups and campaigns and phones ... but Vicidial does not have a "Queue". If you refer to the Queues in asterisk, that's a different story, and worthy of mentioning directly (not vaguely).
now that we're on vaguely ... LOL, you did not mention your Vicidial Build number (required! and important).
Also very worthy of note is that you are using g729 and have only 25 licenses when you have at least 100 calls. So ... how are you regulating the number of g729 calls at 25? Realize, of course, that g729 is a "CPU hog" and will overload your CPU often up to 9X as much as a ULAW (g711) call will, which could be a major issue.
Next we have web usage, if you do not have eAccelerator installed, a mere 10-15 agents could hammer your processor due to the lack of php compression that would ordinarily be provided by eAccelerator.
And last, but not least, why the heck did you Scratch install on 10.04LTS when you could have just installed with Vicibox 4.0.3? (Not a rhetorical question, by the way, I've often found that the answer to this question brings out other issues that can help solve problems ...). If you have the server in a colo, and they will only install Ubuntu Stock for you ... try another colo (LOL). We, for instance, will even install Vicidial for you and maintain the OS and Vicidial install as long as the server is in our facility and being managed by us. But I digress: Use htop to find out which process(es) are hogging your memory. Also find out at what point it gets out of control (10 calls? 25 calls? Number of Agents?).
Are your calls all inbound? All outbound? both? Survey Campaigns?
And what do you mean by 100%CPU Usage? Are you looking at the output from "uptime" and seeing 8.0 in the 1,5,10 minute average readouts? with an 8 processor system, that is 100% CPU usage. Or are you seeing this statistic elsewhere?
Welcome to the Party!