I've heard that it is permissible to shape-up/ line-up the upper part of the beard around the cheek area of the face. Not cutting it off completely but 'defining' it for a lack of a better word. I've always known of this being haraam, that it is not permissible to trim the beard at all.
"The Messenger of God, may God bless him and give him peace, ordered us to trim closely the mustache and leave the beard as it is." (Reported in Sahih al-Bukhari and Sahih Muslim.)
"Trim closely the mustache and grow the beards, and oppose the Magians (fire-worshippers)." (Reported in Sahih Muslim)