Everything is a monopoly if you define the market narrowly enough. The mobile phone market comprises many competing technologies. Apple has a monopoly on OSX, following the same logic we should break up Apple and freely license OSX.
ATT would only be able to "overcharge" to the point that internationals do not buy different phones for use in the US. Consumers would still be free to choose between all existing carriers. And how many internationals does ATT target anyway. Also, I am sure it is a very minute part of its revenue that "overcharging" internationals would cause enough US residents to forego ATT for another US based carrier that ATT would not actually change its pricing structure.
It seems that Sprint is opposing the merger because it wants to reduce competition. Sprint says that it would be too hard to compete with a bigger ATT. The current market structure is easier for Sprint.
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Correct.
But you can also own 100% market share and not be a monopoly as well.
ATT would only be able to "overcharge" to the point that internationals do not buy different phones for use in the US. Consumers would still be free to choose between all existing carriers. And how many internationals does ATT target anyway. Also, I am sure it is a very minute part of its revenue that "overcharging" internationals would cause enough US residents to forego ATT for another US based carrier that ATT would not actually change its pricing structure.
It seems that Sprint is opposing the merger because it wants to reduce competition. Sprint says that it would be too hard to compete with a bigger ATT. The current market structure is easier for Sprint.
It would monopolize the GSM spectrum, meaning it would be impossible to take GSM phones to another carrier and no competition for international roaming (AT&T/T-Mobile merged could set any price they want since all international phones are GSM).
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Correct.
But you can also own 100% market share and not be a monopoly as well.
As to "basic economics", you do not actually have to have a literal 100% domination of a market to be considered a monopoly.