I'm not sure I follow you entirely now. My suggestion was independent of the country. I simply want all my calls to be routed through a single number.
Strangely enough I could do this with a shell script: but simply couldn't make the same thing work by modifying callrouter.cpp.
OK I live in Melbourne, so a full landline number here looks like +61.3.34567890 ('.' separates country/area code/number). It's very common to just think of this number as just 34567890. But if I don't include at least a '03' at the start then my calling service rejects the number as incomplete - though my GSM service would have no complaint. So what I'd suggest is that if a number doesn't start with '+' (full international code) or whatever the local area code introduction is ('0' in most of the world, '1' in North America, '9' in a few places) then a user-specified default country and area code be supplied. Actually some Australian numbers also start with '1' so to make it work you'd have to be able to specify a string of digits rather than a single digit.