I don't think an interview with a developer off-shore must be very different from an interview with, say, a freelance developer from USA. After all, you search for a person with the same profile and the same skills, doing the same tasks.
Still, I noticed personally and often read that Indian developers have a different approach of a relation with a customer. When you ask them to do something which doesn't make any sense or will be overly expensive or has a high risk of breaking something, they will still do it, instead of [politely] explaining to you that you're stupid and don't know what you're really asking.
Since you're a developer, it may not bother you too much. If I were you, I would still talk to them about this point and how they approach it, in other words if they understand that it's better to say "No" to their customer than to implement something substantially broken.
More generally, when you search for a developer, try to determine following things:
Does the person have the right technical skills?
This is done by asking the right questions, and depends a lot of the specific job. It may be something basic, as "What is the difference between stack and queue? Which one do you use to replace a recursion and how?" to something very advanced in a specific language.
Asking to write code is a good idea (see Joel Test), but may be difficult in an interview by phone. You will feel stupid staying at phone waiting for twenty minutes for a person to solve a problem, and it will stress the interviewed person. You also cannot know if the person is actually solving the problem or asking for help on Stack Overflow.
What about communication skills?
Partially you get the idea by talking to the person, but this may be not enough. Often written skill is more important, and you may want to ask if the person has a blog, a high-rep account on Stack Exchange, etc.
Is the candidate THE candidate you want?
This one is the most difficult to answer, and the risk of making a mistake is high (in both ways). Some questions you may ask include:
- In C#, do you use StyleCop? Code Analysis? Code Metrics? Can you talk a bit more about it?
- What are the five things/features you lack the most in your preferred programming language? How would you implement them?
- How much do you spend actually writing code? What do you do the rest of the time?
- Do you use Waterfall? Agile? Can you describe how do you use them?
- Why QA matters? Have you worked with testers? According to you, what do they do?
- If an end user asks you for support with a question you find completely stupid, how do you answer?
- Why the question "Which language is better, PHP or Java?" doesn't make sense?