What are the limits for an engaged girl and boy to tell each other their desires?

Is it permissible for a girl and a boy who are engaged to be married to imaginatively feel and tell each other that he/she wishes to touch the lips, cheek, hair, head etc., or that he/she wishes to put his/her head on his/her shoulder, chest, lap, etc. (that he/she is imagining it at the moment)?

Dear Brother / Sister,

Engagement is not a marriage agreement, but it is a marriage promise. For this reason, those who are engaged are regarded as namahram (not a close relative) for each other and they cannot be together unless there is a mahram (so closely related by blood that marriage with him/her is forbidden) person with them. For this reason, even if they are engaged, it is not permissible for them to be together, to look at the parts of their bodies which are haram (forbidden) to look at and touch each other. And they should pay attention to their talk.
The engaged people have to be careful when they talk to each other on the phone, through msn etc...
For example, if they talk about love, affection, backbiting, lies, and about anything that arouses sexual desires, it is definitely not right.
However, if it is about religious matters that remind Allah, death, hereafter and religious feelings and thoughts, certainly it cannot be said that it is forbidden. The criterion should be as mentioned. When you act in accordance with those criteria, we can say that you do not commit sins and you protect yourselves. Also, we advise you to ask your conscience about what you do. If your conscience is not comfortable, give up what you are doing. 

Questions on Islam