http://www.maxmind.com/app/php
include('geoip.inc');
$gi = geoip_open('GeoIP.dat');
$country = geoip_country_code_by_addr($gi, $_SERVER['REMOTE_ADDR']);
if($county == 'US'){
echo "<code for button>";
}elseif($country == 'UK'){
echo "something else for the UK";
}else{
echo "something else for everyone else";
}