Breakdown of Ovo je poseban uređaj za tvoj mobitel.
biti
to be (sam, si, je)
ovaj
this (m) / ova (f), ovo (n)
mobitel
cellphone
tvoj
your (informal)
Questions & Answers about Ovo je poseban uređaj za tvoj mobitel.
Why do we use poseban here instead of posebni?
Because we are introducing the device for the first time, meaning "a special device". For masculine nouns in the nominative case, Croatian uses the indefinite adjective form (like poseban) when equivalent to English "a" or "an". If we were talking about a specific device we already mentioned ("the special device"), we would use the definite form posebni.
Since uređaj is a masculine noun, why does the sentence start with the neuter word ovo?
The preposition za takes the accusative case, so why do tvoj and mobitel look like they are in the nominative?
They are in the accusative case! Because mobitel is a masculine inanimate noun (an object, not a living being), its accusative form is exactly the same as its nominative form. The possessive pronoun tvoj matches it, so neither word changes its ending.
If the definite form is posebni, why is there an extra 'a' in poseban?