VOIP.ms has great pay as you go rates for both per minute and per SMS message. Ported and some available phone numbers do support SMS, and they have a dedicated texting client for Android and a web SMS portal for computer use, as well as compatibility with other VoIP/SIP clients with built in messaging capabilities. Probably one of the best and lowest cost VoIP providers with texting capabilities, and amazingly full featured and versatile to the point that it's like having your own pre-configured and managed Asterisk server where you only need an ATA or SIP client on your end. About as large and stable and full featured as you're going to get with a VoIP provider outside of "big" tech. They're self-owned, not a subsidiary, been around for over a decade, well reviewed on DSLReports, well documented support wiki, not publicly traded, and based out of Quebec Canada. Rates are as low as 85¢/month for the phone number (paygo inbound) plus 1¢/minute (billed in six second increments), and 0.75¢/SMS with e911 non-mandatory. They even have voicemail transcription, though it costs extra and gets sent to your email, and the ability to manually lock down the number from porting out without the inclusion of a custom PIN of your choosing. It is who we use for our home phone service.
If you want a flat rate monthly service, there's Line2, though they're owned by J2 Global, which really isn't putting that much distance between you and "big" tech, what with them being a part of the S&P 400, and they own eFax, Ziff Davis, IPVanish, etc. This said, they're still basically half the price of Grasshopper (owned by LogMeIn, another S&P 400 tech company) and RingCentral (Russell 1000), with pretty much the same feature sets and capabilities.
