How informal can 为 someone 服务 be？ Recently, I've heard the phrase " 为你们服务 “  used in a number of contexts. It seems like a relatively formal phrase, but I'm wondering how widely it could be used. Could I say, for example,
"我们一下车就有两个人为我们服务“ 
(the example would be at a sporting event with volunteers). 
Is this colloquial? Or would it only work in written, very formal language?
This totally works colloquially.

One of the most famous slogans in Chinese is: 为人民服务 (Serve the people!) - there is not a single Chinese person who doesn't know this.

Likewise you can always 为 XXX 服务, this should be very easily understood by almost anyone.

edit: maybe it would just sound a little pedantic...you wouldn't exactly say that there's two people serving you in English, though, would you...