yes it differs from business to business. You need to find out what your firm's policy on sickness absence is. For more than a few days, you usually need to be signed off by your GP or your occy health department.
It probably depends how your company works. In my company, I get put through to a department when I go sick so that they can offer 'support' if I need it (probably something to do with duty of care) and then they leave me alone. They certainly wouldn`t want to me to keep phoning them to say I`m still off sick. You don`t need to worry about a doctor`s note until after the 7 days but if you were to go to a doctor before that and they decided that you need to be off for longer than 7 days, they would probably just write you a note for the whole period.
We have to ring in 30 mins before we are due to start work and then daily unless it is obvious that you wont be in in for a few days - It's all about keeping them informed so that they can manage the other staff and workloads - But I'm sure each workplaces will have slightly different rules
where I work (NHS) you call in on the day if you are ill, and you can have up to 7 days off before you need a GP note - but if the GP thinks you are ill, he can give you a certificate on day 1. You can't just sign yourself off for longer than a week, not without medical evidence, otherwise you'll be considered to be absent without leave.