1 Question: Is it permissible to chat with girls on the internet?
Answer: If it is feared that they might be drawn towards sin, it is not permissible. Normally chatting ends up in a sin for both sides.
2 Question: I want to ask about talking to ones fiancee on telephone, is it permissible or not?
Answer: If it is feared that you might fall into a sin, it is not permissible. Since she is not related to you through nikah as of now, you cannot express love or start joking and becoming intimate with her.
3 Question: Can I be in a friendly relationship with a girl in my class.
Answer: All kinds of relations with a non-mahram including joking, expressing mutual love, talking with the intention of deriving pleasure, looking at the body of a girl (except her face and hands up to the wrists) and at her hair or looking at her face with pleasure are haram (forbidden). In fact, if it is feared that they might fall into a sin, it is forbidden for them to have any kinds of relationship with each other.