So no, Ericsson cannot set whatever price it wants for its FRAND patents and furthermore cannot charge different rates for different licensees. They cannot charge Apple more than they charge HTC for example.
The rates can be very different.
FRAND only means that similar deals must be available to similar licensees. The rates themselves can vary depending on particulars such as quantity purchased, longevity of contract, credit rating, and cross-licensing.
Especially the latter. For example, Nokia is known to have extensive cross-licensing deals in place, to the point that they pay almost nothing (less than 3% total) in royalties whereas other makers might pay almost ten times that.
Motorola, who invented modern cell technology, used to not even have a patent cash rate at all. There were only two possible deals: either you had to purchase chips and equipment from Motorola, or you had to cross-license everything, in which case the patents were "free".
So yes, they could charge one company more than another. Just not for the same kind of deal.
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Edit: I would add though, that they don't seem to be charging Apple more than others. From Ericsson's similar complaint in a US court:
"
The parties' licensing negotiations have been unsuccessful because Apple refuses to pay a FRAND royalty corresponding to those paid by its competitors for Ericsson's Essential Patents. Apple fails to honor the fact that FRAND licensing is a two-way street, requiring not only that the licensor is fair and reasonable in providing licensing terms, but also that the licensee negotiates in good faith and accepts FRAND terms when they are offered."
Especially since Ericsson has said they'll go along with whatever the court rules as FRAND royalties. You can't get much fairer than that.
Note that Samsung tried to fight a similar contract renewal, but ended up owing almost a billion dollars to Ericsson.