I was wondering if anyone has or had the same issue. I purchased the 520 at the beginning of the month and within the first 3-4 days got my first SIM error. No biggie since the SIM was originally provisioned for an iPhone 4 3G data plan so I called had it provisioned to the Lumia at the 4G HSPA+ data plan. Either way had to shut off the phone, remove and re-insert the SIM to get it up and running again. 3 days later I got the same error again. This time I went to an AT&T store and switched out the SIM to avoid any further issues. Yesterday I went to the movies and the phone was OK going in. After the movie was over, walked out to check the time and again No Service. I had to do the removal and re-insert again and I was fine. Then this morning same thing after being on the charger all night. Since then it has been OK so far. I already contacted Microsoft and was told that since the phone is only 2 weeks old I can go to the Microsoft store and exchange it. I just want to make sure this is an isolated incident before I go an swap it.