Pactolus, Top VoIP Company 2008: FierceVoIP, Fierce 15

Pactolus

Where it's based: Marlborough, Massachusetts
When it was founded: 1999
Website: www.pactolus.com

Why it's Fierce: Pactolus doesn't grab a lot of headlines, but they got on the open-source and SIP bandwagon way early, founding SIPdev.org in the process. Today, the company's SIP/IMS-based apps process 3 to 4 billion minutes of usage monthly in over 140 service provider networks worldwide.  

If you want a service creation environment for SIP, there's RapidFLEX running on industry-standard Linux or Solaris hardware with a supporting XML-based language, XTML (eXtensible Telephony Markup Language).  Don't want to build apps from scratch? There's a portfolio of pre-built SIPWare customizable turnkey services to tap into, including residential/business Class 5 VoIP, large operator-assisted event and reservation-less audio conferencing, prepaid/post paid services and voice messaging.