I use CallCentric.com and I believe they also offer 1-800 number service, if that would be useful.
I am on the "bring your own phone Dirt Cheap" plan and it costs me something like $2.95 a month, and another $1 a month for text capabilities. As I am now back in the USA there is also a $1.50 charge for 911/EMS address listing. At present the text messages to overseas from the USA have to go through their web page portal (they won't forward so far, but apparently they are working on that) but any calls that are incoming are free regardless on my plan. I pay pennies per call for outgoing calls.. They have some plans that charge for outgoing calls, some other plans that include them in a higher monthly fee. I'm not too sure what their business plans are, but you might want to look at them.
I've been with them for quite a number of years and have never had any problem with them whatsoever. Tech support is great, but a bit slow since it's all done through posting back and forth. They have always followed up within 24 hours when I had a question.