IPhone will not automatically connect

I have an Apple 4S phone and when I go to work (we have a guest network we are allowed to connect to and use), I cannot get my phone to automatically connect.  I have asked about it, but I am not getting any results.  I can usually connect after shutting down my phone and turning it back on, then the network shows.  However, I would like it to connect automatically instead of going through this hassle.  I've checked settings and all seems good.  Thanks for any feedback.