I receive a lot of sales calls on my phone. Mainly from IT companies or people selling advertising, and other crap I don't want/need.I politely tell these people to go away, but usually it's not long before some other company calls me instead.And they always have 'withheld' numbers and act like they're my best friend and like it's really really important to me. Some of them I *do* want to keep in contact with, but want to control when and where I talk to them. The problem is that some of the ones I do need to keep in contact with for various reasons are also ramblers who usually take a minimum of 30 minutes to deal with, and then they call you 3 times a week for the next month.I can't change my phone number for various reasons.I have subscribed to the Telephone Preference Service, but it doesn't work.I don't have a PA, so having someone filter my calls isn't an option either.Any ideas for how I can deal with these time wasters? I never know whether I'm answering the phone to a potential client or yet another salesman.It makes a difference to me if I know who's calling. For instance, I don't answer the phone to a client if I'm in the middle of King's Cross with roadworks going on around me or if I have poor reception - it's better to let it go to voicemail in these situations and call back when I'm somewhere quieter. I sort of get stressed out every time I get a withheld number. If I don't/can't answer, I never know whether I'm missing a client call or a sales call. Any tips/ideas for dealing with this?