Try and then update

gistfile1.cfm

<!— Start a call from coldfusion —>
<!— enter your information for the following parameters —>
<cfset api_key="abc123">
<cfset api_secret="abc123">

<!— make the rest request —>
<cfhttp url="https://rest.nexmo.com/number/buy/" method="post" charset="utf-8">
  <cfhttpparam name="Accept" value="application/xml" type="header">
	<cfhttpparam name="api_key" value="#api_key#" type="FormField">
	<cfhttpparam name="api_secret" value="#api_secret#" type="FormField">
	<cfhttpparam name="country" value="US" type="FormField">
	<cfhttpparam name="msisdn" value="11234567890" type="formField">
</cfhttp>

<!— display results —>
<cfoutput>
	HTTP Response = #cfhttp.statusCode# <br>
	<textarea cols="80" rows="10">
	#cfhttp.fileContent#
	</textarea>
</cfoutput>