substring function

I am trying to format a phone number, which may contain an extension....

Here is the node: 
<WorkPhoneNumber>1234567890x333</WorkPhoneNumber>

I am trying to get: (123) 456-7890 x333
In the output (html)

here is my test:

<xsl:if test="string(WorkPhoneNumber)">
<xsl:value-of select="concat('(',substring(WorkPhoneNumber,1,3),')
',substring(WorkPhoneNumber,4,3),'-',substring(WorkPhoneNumber,7,4),substrin
g-after(WorkPhoneNumber, 'x'))"/>
</xsl:if>

This results in: 
(123) 456-7890

Ive also tried this...
<xsl:if test="string(WorkPhoneNumber)">
						<xsl:value-of
select="concat('(',substring(WorkPhoneNumber,1,3),')
',substring(WorkPhoneNumber,4,3),'-',substring(WorkPhoneNumber,7,4),substrin
g(WorkPhoneNumber, 10))"/>
					</xsl:if>

which results in this:

(123) 456-788909090909008080

Im not sure what is happening...

Mike


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