Verizon has more customers than AT&T. That is a fact. Now the market cap fluctuate often so it is hard to say for sure who is worth more in terms of money.
If AT&T trying to buy Verizon, that would cost AT&T over 90% of their annual revenue. It would be like Target trying to buy Walmart, or MCD trying to buy Burger King. In order to acquire a company you have to be MUCH larger than it to make a profit.
What do you think about it ?