If you're looking for a way of making cheap phone calls, you'll have come across new technology called Voice over Internet Protocol (Voice over IP, or VoIP). Most people realise that the decision about whether to use VoIP is really a no-brainer. It allows you to make calls over the internet, instead of through a traditional phone line, so the amount of money it can save you can be significant. But once you've made the decision to use VoIP to make cheap calls, what next? How can you make sure you pick a good low-rate VoIP provider?

If you're convinced by VoIP, but you haven't yet signed up, then don't rush in. Curb your excitement about the thought of all those cheap international calls, take your time and consider the following points.

1. Reputation. Customer feedback is worth more than anything a company says about itself. Does the low rate VoIP provider, as well as offering cheap calls, also enjoy a solid, positive reputation and the goodwill of its customers? Can you find any comments or reviews from existing customers? Some VoIP providers will offer testimonials. What do these say? Are they independent? Perhaps you can find someone who already uses that particular VoIP provider, and who might be willing to give you a candid view about the service.

2. Call plans. Think about what countries you call, and how frequently. Check the VoIP provider's call plans. How many are there? What countries are included? There's no point signing up for a call plan that includes a raft of countries that you're never likely to call, or will call only infrequently. Does the provider offer a basic call plan for UK landlines only, as well as one that includes dozens of countries around the world, and various call plans in between? Beware of a VoIP who offers call plans that simply seem to good to be true – it could be a sign that they're in financial difficulty. Expect to pay from around £6 a month for the most basic, UK-only call plans, and around £20 a month for a call plan that covers numerous countries, with a range of call plans in between.

3. International tariffs. Check the VoIP provider's international rates for calls to countries that aren't included in your call plan. You don't want to have a wonderful, low-rate call plan and find yourself stung by high rates whenever you call a number that's not included in your plan. Fortunately, because VoIP uses broadband to make calls, you'll find that even these rates are much, much lower than those offered by traditional phone companies.

4. Tie-ins and fees. Does the VoIP provider want you to commit to a contract? Is there a trial period? What are the penalties, if any, if you cancel your service? Are there any set-up fees, admin fees, equipment fees, postage fees, or any other kind of charges? And you want to make sure that there is a money-back guarantee, no-questions asked trial period? Check the VoIP provider's website to see how transparent they are about their charges. Ideally, they should be absolutely clear about what you will be charged, and when.

5. Flexibilty. Will the VoIP provider allow you to choose a dialing code? Some will give their customers the option of deciding what dialing code they want – either one that's local to where they live, like a traditional phone service, or one that's local to their customers or family. It might not be relevant to your needs right now, but it could be something that would be of great benefit in the future.

6. Customer service and technical support. What's the customer service and technical support like? Can you contact someone for free, by phone or email, when you need to? Is there someone available to talk to you at any time? Some of the fiercest criticisms of telecoms companies are the result of poor customer service and dreadful technical support. You really don't want this to ever be a headache, should you ever need it, so make sure that the VoIP provider puts the customer first in these respects.

7. Features. What features does the VoIP offer? Traditional service providers often charge for features such as voicemail, call-waiting, caller id, call forwarding etc. Does the VoIP provider charge for such basic features? Or do they offer them for free?

8. Add-ons. What does the VoIP provider offer in terms of chargeable services you can bolt on to your account later, if you want to? These days, thanks to advances in technology, you can get really useful add-ons. You might, for example, be able to make calls from your computer or laptop, add a second phone line, or create a ‘virtual' phone number that rings to your own number, so that friends or family who live abroad can call you cheaply.

9. Transparency and clarity. Does the VoIP provider's site look professional? Is it easy to understand and navigate? Can you find what you want straight away? Is the language clear, concise and unambiguous? Does it inspire confidence that this is a trustworthy VoIP provider?

10. Keep your number. Can you keep your original telephone number if you want to? Is it a straightforward process?

If you're already convinced (and you should be!) by the cost savings of using VoIP providers to make cheap international calls, it's best not to rush into signing up with any old provider. Think carefully about the issues listed above, choose your VoIP provider wisely, and cheap calls will be all yours. You'll never look back.