cheap mobile operators

In EU countries you do not charge for incoming calls to a phone which is located in the country where the SIM is issued (or to be preicise: connected to a network in the country where the SIM is issued - look out in border areas). So what you "have heard"is not true.

I do not think there is any "cheapest" operator - then there wouldn't be others? First of all every operator was many different schemes - some of these will be much cheaper thanothers - but that really depends on the number of calls and SMSes.
International calls cost more or less the same at all operators and schemes as they end up being handled by the same operator. Note that the price to calls to EU are much lower than out of EU. if you have more than a few internatioanl calls / month consider getting Skype (or the like) or real IP-phone.

PS You cannot get a non-prepaid SIM until you have the registration number (Personnummer)form the Swedish authorities - can take months.

well, i understood that no charge for incoming calls.
i did not mean the cheapest as i know sweden is not a cheap country.
i just mean comperatively cheap in sweden.
the second i don t need a prepaid sim as i am not going to remain there for ages to wait for months
for rgistration.i just need a number to have to be contacted when needed.is not it possible
to purchase a number and refill the account every time i want to have balance on my account.

If you are not going for a residence permit but just staying for the 6 months (EU citizen) or 3 month on a Schengen visa, you go for a prepaidSIM (that you "fill up" weith your credit card on the internet or by buying a "fill up card" in any supermarket. Then you have your number that ppl. can call.

Sweden may be a relatively costly country but mobile charges are very low compared to most of Europe. Select supplyer and scheme - they all cost more or less the same. Some big suppliers are telia, tele2, comviq, tre - and then there are all the small without their own network. Find a scheme yo like - look at their homepages (wonder if they are in English - probably not - 99.999% of customers will be naturally be locals for mobile companies ) - so meybe you get a friend or whoever you will work with when being there translate.

ya thanks.i am coming with 3 months shengen viza.