mary,

we've gone over the history ad nausaeum above.

There was not originally a tri-state or anything like it, just a region of the ottoman empire given to British administration as the "Palestine Mandate" by the League of Nations.   The Brits subdivided the Mandate into Jewish Palestine and Arab Transjordan. Transjordan let in some of the Arabs from Jewish Palestine but not all of them. Given that the main purpose of Transjordan was to accomodate those people, it's more than just popular opinion that the Arabs didn't do enough.   

When they realized their solution was not working, the Brits referred the matter to the UN, but first unilaterally granted Transjordan independence.

Transjordan, originally set up for the purpose of being a homeland of Palestinian Arabs, became a state which was eventually renamed Jordan.

THEN the UN decided there should be another subdivision of what remained of Palestine after Transjordan was taken out. That was the divsion into Israel and a Palestinian Arab state in the west bank and Gaza strip. The Jews accepted this proposal, creating Israel. The Arab nations, including the Palestinians in the West Bank, rejected the UN's proposal, wanting all of Israel for their state. They started a war with Israel, which Israel won.

Jordan annexed the land the UN had set aside for the Arabs on the West Bank. In a later war, in which Jordan once again attacked Israel, Israel took that territory from Jordan, creating the occupied territories of today.

The occupied territories have never been a separate state, because their occupants rejected the terms of statehood offered by the UN.

Indeed, there are many who argue, as CarolC notes above in disagreement, that "Palestinian" is neither an ethnic nor a religious nor a political designation, so much as a regional one. The Palestinians, according to this argument, are not a "people" or a "nation" at all, they're just the Arabs living in a given region. As such, they are in a sense interchangeable with other Arabs and thus have no claim on Palestine particularly.

Like CarolC, I don't like or agree with this argument, but probably for different reasons. I personally can accept all of the premises, that they are not a "people" or a "nation," etc. But if they have a regional identity, that to me is significant; "southerners" in the US is an example of the same phenomenon, and some of them feel pretty strongly about it. But there are some foolish Israeli hard-liners who argue that they're all just Arabs, so why can't they live in any of the Arab countries?

Anyway, the short answer to your intial question is "no," there was no Palestinian "tri-state area."

I like the proposal you suggest, however. If the Palestinians would be willing to emigrate it would be an elegant solution.