Any informants they place in your cell with you, regardless of you asking for a lawyer may continue to interrogate you as well. Your prison phone calls can also be recorded and used against you, again regardless if you've asked and not seen a lawyer so if you phone your job and make up an excuse why you won't be there on Monday morning, that excuse can be used against you in court. A well known trick is for the police to place you with an informant who offers you a cellphone, because typically you have to call 3-4 people when arrested (family/gf, job, a lawyer) instead of just the one phone call they have to give you (which they don't have to provide until days after you are arrested). This contraband phone will be recorded hoping you say something incriminating, or just hoping you lie so they can prove later you are a "known liar" since most people don't want to tell their employer they've just been arrested and will lie about it.