The answer to your question is "Legal," by whose jurisdiction and in what country.
In America, it would not be illegal, as long as the address was then truly your, and you in fact could and were capable of being contacted at the address. This is because if you can be contacted there, it is truthfully your address. However, if you could not be contacted at the address, then you would have committed a fraud. Many businesses utilize PO Boxes, or mail services in order to obtain a lawful street address. It is all perfectly legal and a very common practice in America.
I can not speak to the laws of your particular country, as I do not know the laws or customs of your country.
Furthermore, I am not a licensed attorney, and the advice given should not be relied upon or utilized as a substitute for the well reasoned advice of a lawyer, licensed to practice law in the particular state in which you seek to conduct or transact your business.