That, like dumb mouths, do ope their ruby lips
To beg the voice and utterance of my tongue
is this a simile? how?
Yes. It's a simile. It compares whatever "That" refers to to mouths. It also uses the word "like," making it a simile, not a metaphor.
An easy way to remember simile vs. metaphor:
A simile is SIMILAR (like).
An example is:
He fought LIKE a lion (simile).
He was a lion in battle (metaphor -- no LIKE)
If he roared and swung his sword, he acted LIKE a lion. If he turned into a real animal, he WAS a lion.