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Is it necessary to use a comma in a situation when you write...

Not only does the Iphone 5 have many features its predecessor lacks but it also contains many things its competitors lack.


Should there be a comma before the clause introduced by but?

Same example could be found here, although it is less wordy.

Not only is the toy red but it is expensive.

That example would clearly demonstrate the use of no comma.

Thanks in advance.

Yes. Normally independent clauses separated by a conjunction get a comma. But if they're short enough, as determined by the good sense of the writer, sometimes they don't.