Some of these are of the more casual type, friends who see each other from time to time in incarnations and or in the soul realms.  Sometimes in the various gathering areas where souls relax and take their breaks.

Others can be from various projects that souls are involved in, helping each other in various means or just being parts of the projects and visiting and talking during the various parts of the projects and such that souls in groups often do. 

The various activities souls do often involve other souls.  Some of these activities or projects may have some of the same souls that see each other, some will have the souls only seeing certain souls in one activity or project only. 

Soul frienships are deeper then friendships on earth.  The closest to being like a friendship on earth are the most casual aquantinces and some of those may be deeper.

Souls can feel what another soul is feeling even from afar.  Their more empathic by nature then humans are, being telepaths as souls naturally are.  They communicate by telepathy more easily then most humans talk.

Being naturally telepathic and empathic ends in most souls being at least somewhat more feeling about each other.  Though some are more self centered then others and there are those who follow darker roads by their own choice.

Soul friendships are deeper then earth due to the nature of souls.  And relationships that go deeper and farther then friendships are very deep indeed, each of the souls sharing more of their essense and very being with another.