Questions about switching from Verizon to T-Mobile

Currently we have the Verizon 3GB plan ($45/mo) with 4 lines. Two of the phones are on contracts that end this November ($40/mo each) and the other two are off contract ($20/mo ea). With taxes and surcharges this comes out to ~$183.

1). Is there anything I missed about the ONE plan or will it just be $160/mo (plus taxes and surcharges) for 4 lines?

2). Will the deals on phones change after the ONE plan is out? We are going to need 2 new phones and I'm wondering if there will be any promos to go along with the ONE plan once it comes out (possibly a BOGO similar to the one Sprint has).

3). How good of a plan is this? Considering the T-Mobile plan will probably end up running us a little over $200 when you include taxes, fees, and financing for 2 phones. Keeping Verizon @ ~140 a month once all our contracts expire is appealing in the short term even though their data plan is awful.

4). Should we wait and see if Verizon will try offer a competitive plan/price like Sprint did before we switch?