TeliaSonera said demand had been enormous ever since it announced a deal at the end of May to bring the popular handsets to the Nordic and Baltic countries, with 50,000 people in Sweden registering an interest in buying a phone.
Doors open at midnight at the Finnish-Swedish company's main stores in Sweden's three largest cities.
"I really want an iPhone. I want one so badly," Malmö customer Petar Matic told Sydsvenskan.
Matic and his girlfriend Erica Persson have been promised a dinner by staff at the store after they began queuing more than 24 hours before the launch.
And the race is on to see who will be first in Sweden to get their hands on a spanking new iPhone.
Daniel Oskarsson is first in line in Gothenburg, having plonked himself down in front of the entrance to the store at 3am on Thursday.
"There are some things you just have to own and this is one of those things," he told Göteborgs-Posten.
TeliaSonera has promised to provide refreshments and entertainment for all of its eager night-time shoppers.
"Our customers have been longing for the iPhone 3G and we want to give as many of them as possible a chance to buy Sweden's first iPhone 3G at our flagship stores in Stockholm, Gothenburg and Malmö, as well as online," said TeliaSonera's Håkan Dahlström in a statement.
The phones will go on sale elsewhere in the country at 10am on Friday.
An iPhone can only be bought with an in-built subscription of the customer's choosing. For example, an 8 GB iMini with an 18-month subscription will cost 2,495 kronor ($407), plus 299 kronor ($49) a month.