http://www.uesp.net/wiki/Oblivion:The_Doors_of_Oblivion
The book makes an allusion to one person summoning another (although the summoned appears to have refused the summon). I don't know if that's possible simply because they were in two different planes or if it's a "general" rule of thumb. Almost falls under "Recall" in Mysticism as much as summoning. My grossly inflated .02.
that's a real find - not rea dit before
As to th edifference between calling and summoning th ewords seem to say something.
You can call a wild animal all you want - but does that mean it will come to you? I think not normally as a friend, unless you are one of those rare people who have a natural ability to befriend wild creatures. Say hi, say I want to be your friend, and the creature scents something it does not like about you and farts in your face as it hastily departs.
Summoning implies control as stated so that works on the power trip level. A lot of people are very uncomfortable with wild creatures - I would imagine mages, being so highly intellectual, would generally fit into that category, so why would they want to call an animal as a companion if they could not feel they could trust it?