With two big telecom customers, AST SpaceMobile stock looks more buyable -- but it's not yet a sure thing.AST SpaceMobile (ASTS 43.90%) stock is on a roll. Two weeks ago, this tiny telecommunications start-up signed a deal with AT&T (T -0.55%) to provide AT&T customers cellphone-to-cellphone broadband internet connections via AST SpaceMobile satellites in orbit. This morning, AST announced it will also extend this relationship to Verizon (VZ -0.70%) customers.AST SpaceMobile stock jumped 35% on the news (th ...