I keep my phone on silent AT ALL TIMES, for this very reason. Some clients show up early and call to ask for the apartment number; unless I am ready and just kicking about anyway, then no chance are they getting it.
I have some (old and prompt) regs who show up early every time; normally 5 or 10 minutes. In the past I have tried to encourage them to stick to the time. This got exhausting, so now I just make sure I am ready 10 minutes before for these guys. For others, are they hell showing up early. My time is MY time, normally to stuff oat cakes into my starving mouth or guzzle coffee.