<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<asp:Panel runat="server" ID="panelCallButtons">
<table style="margin: 0 auto; vertical-align: middle;">
<tr>
<td>
<asp:Label ID="LabelExtension" runat="server" Font-Names="segoe ui"></asp:Label>
</td>
<td>
<asp:ImageButton ID="ImageButtonUnhold" runat="server" Visible="false" ImageUrl="~/images/unhold-32.ico"
OnClick="ImageButtonUnhold_Click" />
<asp:ImageButton ID="ImageButtonHold" runat="server" ImageUrl="~/images/hold-32.ico"
OnClick="ImageButtonHold_Click" />
<asp:ImageButton ID="ImageButtonTransfer" runat="server" ImageUrl="~/images/transfer-32.ico"
OnClick="ImageButtonTransfer_Click" />
<asp:ImageButton ID="ImageButtonEndcall" runat="server" ImageUrl="~/images/end-call-32.ico"
OnClick="ImageButtonEndcall_Click" OnClientClick="changeImage();" />
</td>
</tr>
</table>
</asp:Panel>
</ContentTemplate>
</asp:UpdatePanel>
function changeImage() {
document.getElementById('<%= ImageButtonEndcall.ClientID %>').src = "images/end-call-32.ico";
setInterval(function () { document.getElementById('<%= ImageButtonEndcall.ClientID %>').src = "images/endcallHover.png"; }, 200);
}
ImageButtonEndcall.Attributes.Add("onmouseover", "src='images/endcallHover.png' ")
ImageButtonTransfer.Attributes.Add("onmouseover", "src='images/transfer22.png' ")
ImageButtonUnhold.Attributes.Add("onmouseover", "src='images/unholdHover.png' ")
ImageButtonHold.Attributes.Add("onmouseover", "src='images/holdHover.png' ")
ImageButtonEndcall.Attributes.Add("onmouseout", "src='images/end-call-32.ico' ")
ImageButtonTransfer.Attributes.Add("onmouseout", "src='images/transfer-32.ico' ")
ImageButtonUnhold.Attributes.Add("onmouseout", "src='images/unhold-32.ico' ")
ImageButtonHold.Attributes.Add("onmouseout", "src='images/hold-32.ico' ")