Zan...there was a thread on here a couple of weeks ago and also on SSCA and others about Globalstar indicating that the service has ALREADY deteriorated significantly and they are leaving users in the lurch and unable to connect from even close in places. Their customers are screaming. Even with "normal" performance...GStar would not be a great choice for the Pacific/Indian Ocean portion of your voyage as coverage is poor.
I know of nothing other than Iridium and Immarsat that can provide true global coverage and Immarsat is hugely expensive since they charge by the bit. BethLeonard and EvansStarzinger have cruised all over using their iridium and need reliable communication for work purposes. They seem quite satisfied but wish it was cheaper.
You already have an SSB right? If so...Pactor/Sailmail may be a viable lternative as Valiente suggests. If not...I would strongly encourage you about the need for an SSB for your trip. I don't think a phone makes up for one.