If your ‘Nokia 3100’ device displays a “No Service” or an “Emergency Calls” only message, this would usually indicate that you are in a location with poor signal strength / limited network coverage.

As a further test however, we would recommend attempting to select a network manually –

“Menu” > “Settings” > “Phone Settings” > “Network Selection” > “Manual” > (Wait for search to complete) > (Choose a network)

If this resolves the issue, please change the network search mode back to “Automatic” when you travel to a new location.