For when you absolutely, positively have to keep your phone switched on but do NOT want to speak to certain people, Call Firewall is a fairly hardcore solution.
It works like many other call barring utilities, but is extremely configurable and easy to fine tune to your required level of chattiness.
Depending on how anti social you are feeling, Call Firewall lets you block everything, block all numbers with a certain prefix (e.g. blocking 07* would make it impossible to receive calls from other mobiles - or if you work in an office with it’s own switchboard you could block any of its extensions)
If you are a bit more friendly you can set blacklists of numbers to block or whitelists of the only numbers you want to let through.
One nice feature is ‘accept calls only from my contacts’ which gives you an instant list of ‘trusted’ people from whom you can accept calls.
thanks