Yes, but there are some exceptions

 If you type in any invalid character the system will automatically reject the SMS, and you'll get this error:

Follow these guidelines and you'll be more than fine:

• Never ever ever copy-paste from Word. You should compose your text directly in SMS Central.
• Almost all characters in a "standard" English keyboard are valid. 
• Accepted
• All alpha characters in the ABC
• All numbers
• All special characters above numbers: ! @ # $ % ^ & * ( )
• General Punctuation characters: - _ = + [ ] { } / \ < > ; : , . 
• Apostrophes: ' "
• Tilde: ~
• (whitespace)
• Not accepted
• The vertical separator:  | (this is the character above the backlash ( \ ) in the keyboard).
• The inverted apostrophe: ` (this is the character below the tilde ( ~ ) in the keyboard).