Nokia’s Network Setup app for Nokia’s Windows Phones is coming back to Marketplace, apparently. Personally never saw the app being removed from Nokia Collection and used it on multiple Lumia phones in the past 6-7 months.
It could be that this only concerns Lumia owners in North America. Whatever the case is you should see Nokia’s own Network Setup app to appear to your Nokia Collection in following weeks, if you don’t already have it.
I can now let you know that a new version of the Network Setup app will be reviewed this week to go live and it should be published worldwide later this week (wk24). Please be aware that propagation through Marketplace may take an additional 3-5 days after the app is published. – Nokia Support