“为服务”是in service 还是for service?

应该是 at service

具体想表达什么意思呢？

一般想为谁服务，不用service，而用serve。

例如：It's my pleasure to serve you.很高兴为您服务.

I'll be pleased to serve you.我很乐意为你服务。

Could I serve you anything else?还需要我给您点什么吗？

是 at sb's service，例如：I'm at your service.

为xx服务：service for sb

for service