Need Regular Expression

For you question this regex will do:

^[0-9\+\- \(\)]{10,25}$

But! To check phone number it definitely not good, as it allows the plus sign to appear anywhere, allows unclosed parentheses...
So if you want to check phone numbers you may split it to two. One for a regex to check that no invalid char are in the input, and one other to check syntax...

^[+]\d{2}\s[(]\d{3}[)]\s[\d]{5}-[\d]{5}$

Have a look at the samples on http://www.regular-expressions.info/reference.html[^]

Here for international phone number matching https://support.sonus.net/display/UXDOC31/Regular+Expressions+for+Number+Matching+and+Transformation[^]

check following
^\(?([0-9]{3})\)?[-. ]?([0-9]{3})[-. ]?([0-9]{4})$
^(\+91[\-\s]?)\d{10}$

you can use ajax

<asp:toolkitscriptmanager id="ToolkitScriptManager1" runat="server" >
    </asp:toolkitscriptmanager>

 <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
    <asp:FilteredTextBoxExtender ID="FilteredTextBoxExtender1" runat="server" TargetControlID="TextBox1" FilterMode="ValidChars" FilterType="Custom" ValidChars="+()-0123456789">
    </asp:FilteredTextBoxExtender>

FilteredTextBox