Is praying silently really praying?

I enjoy the fellowship of going to prayer meeting during the week and praying out loud with the other folks at our church. It is edifying, and also a good way to learn how to pray.

But Jesus said this about praying:

"And when thou prayest, thou shalt not be as the hypocrites are: for they love to pray standing in the synagogues and in the corners of the streets, that they may be seen of men. Verily I say unto you, They have their reward.
But thou, when thou prayest, enter into thy closet, and when thou hast shut thy door, pray to thy Father which is in secret; and thy
Father which seeth in secret shall reward thee openly.
But when ye pray, use not vain repetitions, as the heathen do: for they think that they shall be heard for their much speaking.
Be not ye therefore like unto them: for your Father knoweth what things ye have need of, before ye ask Him." Mt. 6:5-8

He doesn't say though that one must either pray out loud or only in your mind. Either way the Father hears you. Of that I am sure.