(Actually you might prefer to call this a "description-confusion trick" since Jehovah calls himself Protos kai ego meta tauta - "First and I [am] hereafter" - Septuagint, Is. 44:6; whereas Jesus calls himself ho protos kai ho eskatos - "The First and the last" - somewhat similar descriptions but much different wording or title. (Is. 48:12 is sometimes used , but it says in the Septuagint that he is: protos, kai ego eimi eis ton aiona - "first, and I am into the ages.")
Is. 44:6 - "Thus saith Jehovah, ... I am the first and I am the last; and besides me there is no God .... (:8) Is there a God besides me? ... I know not any." - ASV.
Rev. 1:17 - "... And he laid his right hand upon me, saying, Fear not; I am the first and the last, (:18) and the Living one; and I was dead, and behold, I am alive for evermore, and I have the keys of death and of Hades." - ASV.
The trinitarian "proof" goes like this: "since only one can be first (and last), and since Jehovah is `first' (and `last') and Jesus is also `first' (and `last'), then they must both be the same one!" Therefore, they say, Jesus must be Jehovah!
The answer is, of course, that there can be many who are "first and last." We must discover, from context, in what sense they are "first and last."
For example, in the Biblical understanding of the meaning of the term "first and last" (or "only"), Adam was "the first and last" human created from the dust of the earth. But calling him "the first and the last" would certainly not mean he is Jehovah, and it does not mean he is Jesus (although any devious Bible student could find such "evidence" at 1 Cor. 15:45)!
We could certainly call Jesus "The first and the last" because he was the first and last (only) direct creation by Jehovah himself. The rest of creation from Jehovah came through Jesus. But, instead of speculating on the many ways Jesus could be considered the "first and the last" (only), we need to examine the use of "first and last" in context to discover in what sense it probably was intended originally!
Examining Is. 44:6, 8, we see that "first and last" refers to Jehovah being the only person who is the Most High God: "I am the first, and I am the last; and besides me there is no God ... I know not any." - compare Is. 43:10; 2 Sam. 7:22; Deut. 4:39.
Now if we examine Rev. 1:17, 18, we can see in what sense "the first and last" (only) is intended there. Context shows that it is not (as it could have been) in the sense of the only direct creation by the Father, Jehovah, and it is certainly not in the sense of the only true God (John 17:1, 3), but it clearly refers to the resurrection (the dying and then living again) of Jesus!
Notice that the entire context refers to death and living again: Rev. 1:17:
"I am the first and the last, (:18) and the living one; and I was [or `became'] dead, and behold I am alive for evermore, and I have the keys of death ..." - compare Rev. 2:8 (the only other place Jesus calls himself "the first and the last").
Jehovah, the Father, uses the expression at Rev. 22:13 - and makes no reference to dying and living again, apparently intending it as he did at Is. 44:6 - "I am the only God."
So in what sense is Jesus the first and last (only) resurrected person? Just as he was the first and last (only) of Jehovah's direct creations (and all other things were created through Jesus), so Jesus was also the first and last (only one) of those resurrected to eternal life who was resurrected directly by the Father (Jehovah) Himself (and all others are to be resurrected through Jesus who now has "the keys of death") - see John 6:39, 40; Acts 3:26; Acts 13:30, 33, 38.