I worked for SAI Global for 18 months, headquartered in Sydney, Australia with offices in 27 countries, while I was in Atlanta, GA, US. Now I work for SunTrust bank with a lot of teams in India or split between India and the US. Even my own small business in the 2008-2013 range had clients in the UK and Australia.
If you can do a face to face meeting every now and then, or at the very least once at the start of team formation, it goes a long way towards keeping the bonds strong enough for phone and webcam meetings to be more effective. But I find these opportunities to meet and form bonds in person work like batteries that over time lose their charge, so try not to let a year go by at the most without spending the money to do it again. Also, teams do change given enough time due to personal reasons if nothing else, so there will be teammates that have never met in person and may never find the chance. So annual meetings will take care of that situation. Of course, do it more frequently if you can. The productivity boost is worth the expense; hard to measure but gut feel and experience tell me that this is true.
Otherwise, collaboration tools like Slack work in both synchronous and asynchronous mode, if you will. Of course, you have to identify overlap hours. Webcams are a must as well. There are really great ones that follow speakers around the room but cost like $6,000 USD. For something closer to $200 USD you can get a fish eye lens webcam that can manage to put the whole team in the room in an OK manner; complement that with a great microphone like the Blue Snowball USB microphone for about $69 USD. I’m sure there are other mics but this one has just 3 settings for picking up sound and that simplicity plus the quality of the mic make it a great choice. Several of us on the Agile Uprising board own one and use it for podcast recordings solo or with groups, just change the setting to fit the situation. The mics on cheap webcams usually aren’t good enough on their own.
For distributed Scrum teams, I have had to use proxies in each city being the ones to keep a tight bond via phone and Internet. So a Product Owner in the US would have a Product Owner proxy in India. They would meet enough daily to and use a common electronic backlog tool and common information radiators. Not ideal but workable.