How long a UK resident can stay abroad is up to the country the person is visiting. For example, a UK resident can stay in the United States 3 months without a visa, and longer with one. Some countries will only allow him to stay there two weeks, and many countries require the UK resident to obtain a visa before traveling. The visa will specify how long he may stay.
If what you're asking is how long can a Polish immigrant stay for in the UK, the answer is: infinitely. Both the countries are in the EU and EU nationals can visit and stay in each other's countries without limits. If an EU immigrant, including Poles, were to live in the UK long enough (a few years), they might be eligible for the status of a Resident or - to apply for a British citizenship.
It will depend on whether you are European citizen or not.
If you mean calling it from a UK mobile while abroad... you would pay whatever your network's roaming charges are. Most UK based mobile operators have a list of countries where roaming is now the same as in the UK (FREE if you are uk resident). You will also have to check that 03 numbers are within your inclusive tariff
If you have dual nationality, you can stay for as long as you want to and can afford.
Indefinitely
As long as you like, there is no time limit. Any UK citizen can leave the UK at any time and stay away for the rest of their life, if they want to. The reverse question is important, how long will the country you go to let you stay there? A UK citizen has the right to live and work in any EU country for as long as they like. For any other country you will need permission to stay there permanently (visa, residence permit, work permit). Finally you will need to renew your UK passport eventually. You can do this at a British Embassy by post. You do not need to return to the UK for this.
In the UK, it will stay for about two months :)
3 to 4 weeks
It depends on the context. Scotland is a part of the United Kingdom, so in that sense it is not considered abroad within the UK. However, if you are located outside of the UK, then Scotland would be considered abroad.
A UK Resident is someone legally living in the United Kingdom, meaning you would have a British passport.
5years
11 years