I used a sony ericsson for about a year, and there was no setting to restrict calls. I know this because there was this one guy who would not stop texting me, and so I tried, but it's not an option. At least not for my sony ericsson, it's possible you have a different model and you can but I really don't think so...
Go on settings, then scroll across to calls then scroll down to manage calls then restrict all incoming or whatever, activate it then your good for a cup of tea!