What Do Symbols On Samsung Galaxy S3 Mean

What does the symbol x mean by my text messages on my, My samsung galaxy ace will not accept incoming text messages, it keeps saying message memory full, i have cleared my phone, deleted all my messages?. What does the h symbol on samsung galaxy s mean ? - there, What does the h mean on top of screen,also red and green arrow. its changes for h to 3g but mostly on the h. its not in the manual. please help?.