The corporate version of Google’s application suite will now get a 99.9% service-level uptime guarantee, dragging the search company and would-be communications and applications provider in line with the more demanding service delivery environment of carriers and enterprise hosting companies.

Google offers free versions of its Apps – including Gmail, Calendar, Docs – to consumers. But it also sells a $50 seat-license version to corporate users that make a large commitment to the platform. The service level agreement (SLA) targets that “premier edition” of the Google apps suite.

Details of the SLA can be found on the Google Web site. Essentially, Google is promising compensation if service downtime exceeds 45 minutes per month. One caveat: It won’t count toward this total outages of less than 10 minutes, a clear compromise from more demanding carrier enterprise SLAs, where “five nines” reliability means outages are counted in seconds, if not minutes.

As for compensation, Google said it will add three days of service to the end of a contract for 99% uptime, seven days for 95% to 99% and 15 days for less than 95%.

The uptime guarantees come as Google earlier this month suffered a significant outage to its Gmail service, with some users unable to access email for up to 30 hours. That outage drew howls of complaints on Google user groups and pointed to the risk in putting mission-critical services into a hosted, or cloud, environment, especially one without the very strict SLAs typically offered by service provider and enterprise hosting companies.