Is this a test or a SV requirement?
I've had to do this a few times for SV, as it seems to be a common thing in UK telcos to convert from msisdn to ctn
Firstly, look at your High Level Design (HLD) document, to determine whether the business requirement is that the msisdn is always going to be 12 digits beginning with the UK country-code.
Then, look in the HLD (or Low Level Design document) to determine whether msisdn is ever used in a response.
The answer to those questions determines how you deal with the conversion.
If it always begins with "44", and if msisdn is never used in the response, I would add a scriptable request-side DPH, doing something like this (not syntax-checked):
import com.itko.util.ParameterList;
import com.itko.util.Parameter;
ParameterList args = lisa_vse_request.getArguments();
msisdn = args.getParameterValue("msisdn");
ctn = msisdn.replace("44", "0");
args.removeParameter("msisdn");
args.addParameter(new Parameter("ctn", ctn));
lisa_vse_request.setArguments(args);
If the rules for msisdn are different, you will want to use a different string replacement routine, perhaps something like:
ctn = "0" + msisdn.substring(2, msisdn.length());
Regenerate your virtual service with that scriptable DPH, and your request arguments will now include "ctn" instead of "msisdn", and your response will include <ctn>{{=request_ctn;/*07997300156*/}}</ctn> instead of the raw value.