Siris Capital Group LLC said Sept. 10 that it agreed to buy Premier Global Services Inc. (PGi) for about $1 billion. Siris has agreed to pay $14 a share cash for each PGi common stock. The deal includes a go-shop where PGi can solicit bids from third parties for 45 days. Atlanta-based PGi provides collaboration software and services. Barclays Capital Inc., SunTrust Robinson Humphrey, Inc. and Macquarie Capital (USA) Inc. are providing debt financing. Allen & Company LLC provided financial advice to PGi while William Blair & Company and Evercore advised Siris.