Depth of experience in a given sector or vertical, evidenced by exposure of x,y,z projects in that sector/vertical is the important piece; it really dosen't matter too much whether that major change programme (or whatever) in telco/mobile was with Orange, Vodafone or BT - if the client is FTSE100 say so, if its FTSE250 say so (and big it up a little).Never disclose confidential clients on a CV; if you meet with a senior hiring manager at interview and they want the information you could tell them verbally.