There's no such thing as "conventional" English.
There's standard English, and also formal English and informal English. There are also dialects. The rest is just idiocy.
1. My wife and I went to the movies last night.
This is standard English.
2. Me and my wife went to the movies the other night.
This is totally wrong but perfectly acceptable.
3. A friend called my wife and I the other night.
Idiocy. Wait, it gets worse:
4. I reserved seats for my wife and I.
Thing is there used to be, and still is, a rather large group of people (an entire class in fact) known as the Philistines. (Well, they used to be known as the Philistines: the word is all but forgotten today because Philistines are easily offended while constituting a significant portion of the electorate).
They wish to come off as "educated" ("genteel") without actually learning anything. They believe they can get away with a few adjustment to their speech and manners. Someone explained to them at some point that "me" was wrong and "I" was right. They pounced on it. To this day they're convinced that so long as they say "I" where their instincts urge them to say "me," they'll come off as "educated" ("genteel") and will be able to condescend to anyone who says "me."
The problem with that approach is that sometimes saying "I" instead of me is correct, and sometimes it isn't. Oh, and there are instances when neither "I" nor "me" applies, and one actually needs to use "myself" instead. Don't tell the Philistines, their heads will explode.
Earnest and intelligent discourse on the English case system is all but impossible today, for various reasons.
The rule of thumb is you can arrive at the correct way of saying things by locking the wife up in the closet for a moment.
A friend called I the other night.
I reserved a seat for I the other night.
Both are clearly idiotic. That's because when the action is directed towards you (i.e. when the case is not nominative), you must use "me," and sometimes you must use "myself" (as in "for my wife and myself").
Another way to look at it is to remember that you should use "me" where you would use "her" and "him," and "I" where you would "she" and "he." (Try saying "A friend called my wife and she the other night." Stupid, right? That's exactly how people sound when they say "A friend called my wife and I the other night."
A Philistine is a person whose position in the food chain exceeds their cultural and/or spiritual level.
Something like that.