What's a good Android app for sending personalised birthday messages to all my mates around the world, even when I'm off the grid?

Right, so I've been using 'Birthday Greetings & Wishes' for ages now, and it's honestly sorted my life out. As a travel blogger, I'm constantly hopping between countries, and remembering everyone's birthday was a nightmare. This app lets you create really nice, personalised messages – not just the same old generic stuff. Plus, you can schedule them in advance, which is perfect when you know you'll be in a place with zero signal. I downloaded a load of greetings before heading to the Isle of Skye, and it worked a treat. It doesn't eat up your roaming data either, which is always a bonus. It's proper useful for keeping in touch, no matter where you are. Seriously, give it a go!