Yes that is possible. You have not said which ITSP you are using. As GV sends CallerID in a different format from most other providers the following is slightly more complex than it could be.
1. Go to the 'User Settings, User Defined Digit Maps' page. Choose an unused one, possibly #2. Give it a name by editing the 'Label' entry. Your choice but I suggest acc. (Short for accept). Note that you should enter acc, not Macc.
In its DigitMap field enter the list of the numbers that you want to accept in the area code you want to block. The entire list should be within a single set of ( and ). Between each number use a | as separator. Each number should be of the form
@x.4567890
where 4567890 represents the last 7 digits of the number, ie no area code.
So a three number map would look like
(@x.23456789|@x.8881234|@x.4325566)
Save that. (Submit button.)
2. Go to the 'Voice Services, SPx' page (x is the SP number you are using, probably SP1 if you are using just one provider.) Change the 'X_InboundCallRoute' from the default ph to
{(Macc):ph},{(<+>:)x.abcxxxxxxx:()},{ph}
where the acc in Macc is the label you used for the User Defined Digit Map and change abc to the 3 digit area code you want to block. There are 7 x after that.
Save that. (Submit)
