Les1, you must look for a provider that offers an "app" for your smart phone.
VOIP providers can be placed in the following categories:
- Computer Only (e.g. a mentioned VOIPcheap.com) - you must install an app on your computer and use a headset
- ATA device & Computer - you must use your own ATA (analogue telephone adapter) that connects between the Internet and your regular telephone (it's like a converter box) + you can use the service on a computer using any freely downloadable VOIP software.
- Proprietory ATA only - you must use ATA offered by the service provider - e.g. Vonage, Lingo, Magicjack, and several others
- Wholesale - you must use a dedicated IP and prefix authentication. This is service offered to telecom carriers and phonecard providers. E.g. voxbeam.com
At the beginning of VOIP, computer-software with headset was the standard. Now the standard has shifted, and the most commonly used providers among people are those offering service via ATA. You usually are issued a SIP username and password to authenticate. So you can use the service from any VOIP device (ATA). These providers also offer service from softphones (software that you install on the computer and use headset) where you enter the issed SIP username and password so you can use the service when you travel from your laptop, etc. In recent two years, with the proliferation of the smartphones, these providers started to offer "apps" for smartphones. Most common apps are for Iphone and Android, not so many for Symbian or Blackberry. Again, these "apps" work with SIP username and password for your account, so you enter those after you install the app, and you are ready to go.
One of such providers is VOICEBUY.com which I use. They have great rates, 3 routes (standard, premium, and super premium), and offer mobile VOIP for all major smartphone types.
Voicebuy Mobile Dialer & Mobile VoIP Solutions | Voicebuy VoIP Provider
Minimum topup is 25 dollars, but there is no minimum to use per month. You can sign up form the DR, and use a DR or international debit or credit card (debit card must be enabled for Internet transactions). You can also use PayPal. Credit card payments are routed through Moneybookers (Skrill) or PayPal.
One more word of advise - use only where good Internet coverage is available. While it may be tempting to use from 3G data network of wireless carrier (Orange, Claro) the quality will not be so good, and spotty at best. So use WIFI fixed Internet coverage (Wifi connected to DSL, for example).