I want to play against my friends on Ticket to Ride but I wondering if I can if they are on their iPhones and I am on my iPad?
Yes, all iOS versions of TTR may be involved in a multiplayer game, but only with expansions that are available on all devices.
As official site says, you may:
- Online Play (WiFi or 3G) against other iPad, Android, Mac and PC gamers with Days of Wonder Online support
- Players can challenge rail barons playing on other platforms including Steam PC and Mac, Android, iPad, and on Days of Wonder's online portal
They did not say exactly about iPhones, but I think they did not make special version for iPhones only.