We’ve become so used to asking for — and getting — free WiFi that it’s almost become expected every time we travel.

But it doesn’t happen very often when we fly. There are exceptions.

JetBlue has offered free WiFi for a while, and some airlines like Alaska and Delta have begun to offer free in-flight messaging.

But now, Delta is beginning to test the idea of free WiFi system-wide. Delta started a free WiFi test in May on 55 of its domestic flights, and the plan is to introduce it across its entire route network soon.

One caution is that while it’s nice to have free WiFi,  if you don’t have the right bandwidth on the plane, the WiFi — and the flight — can seem painfully slow.