Yes, it's perfectly possible. You don't pass parameters to php functions. Instead of that, you use HTTP protocol to execute php scripts.
You need to execute a GET HTTP command from your mobile device like this:
http://your.app.server.com/imei_script.php?imei=IMEI_VALUE
In your PHP script, you will have something simple like:
<?php
// to return plain text
header("Content-Type: plain/text");
$imei = $_GET["imei"];
// make a DB call to check if IMEI exists
// store "true" or "false" string in $retval
echo($retval);
?>
Your PHP script will reside in your application server (Apache with MOD_PHP). Refer to Apache's documentation to setup it with PHP support, and to learn where to place the script. You will have to add the DB part. There are lots of examples you can find on the internet (even in StackOverflow) to learn how to connect to a Database with PHP. They all depend on what database you connect to, so when you search (or ask in StackOverflow), make sure you specify what DB you are connecting to.
To invoke remote HTTP commands with Java ME you can use HttpConnection interface.
You will use something like:
String imei = ...;
String url = "http://your.app.server.com/imei_script.php?imei=" + imei;
// This will remotely call your PHP script with the IMEI parameter you need
HttpConnection c = (HttpConnection)Connector.open(url);
