I know how you feel mate. I fight this battle every day. I work in a client facing role within investment banking so struggle bad with clients at times on certain names that begin with B, W etc. My advice to you is two-fold 1) increase your inner confidence. Quick way to do this is to improve your appearance. Can do this in many ways. Gym, better fitting clothes, haircut (heck even trimming body hair will do it). Doing this will make you have more belief in yourself. 2) Try removing the first letter of the word you can’t get out. I don’t know where you work but suppose it’s Walmart and W you get stuck on. When you answer the phone say ‘good morning, ‘All-Mart’. No-one will realise or call you out. I’ve been doing this for ages on people’s names with letters I get stuck on. No-one notices. This is a good workaround. Good luck mate. Keep fighting the good fight. Don’t let the stammer silence you.