Telepathy has huge social implications, depending on it's nature.
There would likely be times and places where it is considered appropriate to use telepathy, and times and places where only vocal speech is considered appropriate, and times and places where *only* telepathy is considered appropriate. Words spoken aloud might be considered 'for public consumption' while mental speech is 'private.' A town crier would stand in the square, reading off his proclamations, but in the royal court, silence reigns as a half-dozen courtiers are engaged in private side-conversations that cannot be eavesdropped upon. Inside the home, kids play, while their parents have a frank conversation 'over their heads.' The teacher speaks upon the subject of the day, knowing from long experience which students are focused upon her words, and which are focused entirely upon their private conversations with the objects of their affections.
Many of the features of the modern internet would be present. Just as the man on the laptop in the restaurant could be engaged in dirty chat with someone, so to could the 'absent-minded' young noblewoman be having a psychic tryst with that equally distracted-looking sweaty gardener (who is notably not her husband) over yonder.
Anonymity would also be a feature. In the real-world, many found the nerve to speak hateful or threatening words to Jews or Gypsies or homosexuals, but in a world where one can send a hateful *thought* to someone, and remain unseen, and have no one else 'witness' this threatening or harassing behavior, all sorts of 'bravery' will appear in the people who would otherwise have scowled but held their tongue. The despised minority will 'hear' threats and insults all day long, and not know which of the people glaring at him are the sources of these comments. Many of them may come from people that can see him (from a second story window, or across a crowded marketplace) but whom he cannot quickly locate to identify. And, as a member of a minority, it's not like he can run to a judge or guardsman, even if he did identify the source of the threat, as it's 'his word against theirs,' since there would be no witnesses to this sort of speech, and in this sort of 'he said, she said' situation, the despised minority always loses the case.
If line of sight and / or line of effect is not required, and a telepathic conversation can be held through walls, the use of 'speakers' may become commonplace among the wealthy. Going to meet the nobleman that has hired one's services, one would be led to a room with an attractive young man or woman who would greet you on behalf of Lord Whathisface. She would have a 'script' of what the Lord wants said to your group, and in the event where your line of conversation goes 'off-script,' she would close her eyes for a second, contact the Lord, clarify things, and then proceed 'speaking' for him. In noble courts, these speakers would be referred to as Seneschals, and speak 'with the voice of the king,' but wealthy merchants would be as likely to use such. Indeed, a wealthy young noble may not even directly meet her *suitors,* but instead speak to them through such a proxy, leaving a suitor in the awkward position of not even knowing what the woman he has 'spoken to' on several visits actually looks like, or, in a Cyrano de Bergerac fashion, end up falling in love with the speaker, instead of the woman she is speaking for!
Even if line of sight is required, the use of 'one way mirrors' or walls with see-through frescos or construction (such as those little walls that stand between a priest-confessor and his parishioner, obscuring things, but not blocking line of sight) would be an option. The king can see into the room, from who knows where, and his words can be heard by his Seneschal, who can then convey them to those who stand in his presence.
Depending on how easy it is to 'lie' using telepathy, it is possible that someone with severe ADHD, who finds it difficult to 'tune' his thoughts, might end up having the psychic version of Tourette's Syndrome, prone to blurting out whatever comes to mind as he attempts to telepathically 'speak.' Such people would be considered embarassments, and be socially ostracized and unlikely to engage in mental speech, because of their 'handicap.' On the other hand, in some situations, they may play the role of 'wise fool.' Knowing how difficult it is for such a person to engage in deception, a nobleman might prefer the 'plain speech' of his 'fool' to the oily twisted elocutions of his courtiers. Just as the 'wise fool' in primitive cultures found themselves the only person in a tribe able to actually tell the chieftan when his plan sucked, since they had no status to lose, the 'psychic tourette's' sufferer might be considered a 'truthspeaker,' and be a valued messenger among people who have reason to prefer a message that they can trust, rather than a pretty-sounding one.
The Duke may have to hold his temper listening to the young lad psychically digress about that enormous mole on his cheek and whether or not it was really true he had the last person to mention it drawn and quartered and how visible his wife's cleavage is in that dress, but at least he can be assured that the young man isn't lying to him when he says that the Baron wants to arrange a private meeting to discuss bumping off that annoying Count to the north and splitting up his territory by having his kids marry their own at crossbow-point before the King hears about it.
Telepathy also has potential as an interrogation tool. Even if limited to mind-speaking, and not actual mind-probing, a prisoner could be subjected to constant telepathic 'noise' during his confinement, left unable to sleep or concentrate until, after several days, he is a babbling nervous wreck, and a professional can be brought in to coax useful intelligence from his ramblings. Presumably mental speech is as tiring as verbal speech, so the guards can't just mentally sing 'Henry the Eighth, I am' or 'This is the song that never ends' for eight hours straight, but smaller shifts would be quite likely. Every hour another pair of guards show up for a single hour shift, and commence singing bawdy tunes to the prisoner, or reciting documents detailing the prisoners crimes and the archival records of what happened to the last prisoner executed for said crime...
"After an hour in the Spanish chair, Malvolio's feet were swollen and red, and he had stopped producing tears, although sobs still wracked his body, betimes. The skin had cracked and the juices sizzled as their crossed his flesh. He had entered a state of constant shuddering, as if his body was falling to pieces within, and the brazier was removed, and his feet plunged into a bucket of iced water, whereupon great convulsions racked his body, so severe that he broke one of the arms from his chair! He had ceased screaming some time before, but again a great cry of anguish tore from his throat and the flesh peeled away from his feet in clumps, forming a loathsome stew. Finally he shuddered once and fell dead shock to the body and perhaps even mortal terror. Justice was done, and I removed myself from the chamber, sickened by the smell of meat and the rumbling it incited within my traitorous belly."
After three days of constant mental haranguing, the prisoner would be delerious and babbling, easy prey for a professional interrogator, with no need for actual physical abuse, and no fear that an overzealous guard will 'accidentally' kill him and thus deprive the authorities of any information that they need from him.
