Jepp Int'l Handling is like most others in the business. They contract with local airport handlers and coordinate everything. Having a service always on standby and briefed on all of your plans, pax info, special needs, makes it easier to get things changed at the last minute or while enroute. Can communicate many many ways including via AIRINC which is handy for inflight messages. Also a 24 hour service so time zone adjustments do not complicate things.
Jepp, Base Ops, Universal, Colt, and a few others all compete for the same customers.
Of course there's the DIY route and this works too but can have its limitations.