Samsung Galaxy Apollo disconnecting?

My Samsung Galaxy Apollo mobile is new, but several times already I have lost my service because either the SIM card has popped out, or it has disconnected itself (needing a restart.) I miss calls and when I eventually realise the phone is not connected and sort it out, I get a bunch of voicemail messages and texts come through.

I'm wondering if anyone else has had this problem and if there is anything else I can do.