There shouldn't be any need to install Web Access. You can do everything client-side using the existing NameCtrl persona menu - this is the pop-up menu that gets displayed in SharePoint (and other web-based apps like Dynamics CRM) when hovering over a users presence icon. This menu allows you to call the user, start a new conversation etc. You'd need Office installed on the machine you are running on in order for it to work.
As an example, try this on any client machine running Office 2007/2010 and IE. Hover over the "Your Contact" text to see the persona menu (your site will need to be added to the Trusted Sites or Intranet zone):
<script>
var sipUri = "your.contact@your.domain.com";
var nameCtrl = new ActiveXObject('Name.NameCtrl.1');
if (nameCtrl.PresenceEnabled)
{
nameCtrl.OnStatusChange = onStatusChange;
nameCtrl.GetStatus(sipUri, "1");
}
function onStatusChange(name, status, id)
{
// This function is fired when the contacts presence status changes.
// In a real world solution, you would want to update an image to reflect the users presence
alert(name + ", " + status + ", " + id);
}
function ShowOOUI()
{
nameCtrl.ShowOOUI(sipUri, 0, 15, 15);
}
function HideOOUI()
{
nameCtrl.HideOOUI();
}
</script>
<span onmouseover="ShowOOUI()" onmouseout="HideOOUI()" style="border-style:solid">Your Contact</span>