There are at least 840,894 Android apps available today, according to AppBrain. I suspect a few of those have slipped past you. Until recently, I hadn\u2019t heard of the apps I\u2019m about to recommend. But all of them are worth a prompt download. (You may also want to check out my last post, "3 Must-Have iOS Apps You\u2019ve Never Heard Of.")\u00a0\n\tPostagram Postcards (Free)\n\tI don\u2019t send traditional postcards to friends and family when I travel. I send Postagrams.\n\t(Screen shot: Sincerely Inc.)\n\tPostgram is an\u00a0iOS\u00a0and\u00a0Android\u00a0app that lets you turn smartphone pictures into snail-mailed postcards. You can also add brief messages to your images. Though the app is free, you pay a fee for Postagram delivery, which includes postage: $1 per card in the United States and $2 for international addresses. Photos can be popped out of the postcards, too, to make 3 x 3 prints.\n\tUsing Postagram is fun and easy. You just select a pic from your phone\u2019s photo library, Instagram, Facebook, or Dropbox; add the appropriate mailing addresses\u2014you can send the same card to multiple people; and you\u2019re done.\n\tPersonalized postcards can mean more to recipients than generic cards. Another potential use: The next time you\u2019re invited to a party, take some fun pics of the hosts with your iPhone. When you get home, turn the best pic into a Postagram and send that instead of a traditional thank you card.\n\tKey Rings Reward Cards (Free)\n\tYou know those loyalty cards dangling from your keychain or stuffed into your wallet? Ditch them right now, and download Key Rings Reward Cards for\u00a0Android and iOS. The app scans each loyalty card\u2019s barcode. And you can also take photos of cards' front and back sides, which is a good backup idea in case a retailer\u2019s scanner can\u2019t read the loyalty-card barcodes on your smartphone screen.\n\tIn addition to freeing up your keychain or wallet, the app lets you enroll in new loyalty programs; search for offers based on location and retailer; review weekly sales circulars; and create shared shopping lists. Key Rings brings you one step closer to transforming your smartphone into a digital wallet. One caveat: You can\u2019t add a lock code for extra protection, as you can with some similar apps, including Mint.\n\tSlydial (Free)\n\tWe\u2019ve all been there. You want to leave a voicemail, but you don\u2019t want to actually talk to the recipient. It\u2019s probably nothing personal; you just don\u2019t have time for a conversation. Or it may be too early\/late for the person you\u2019re calling.\n\tThat\u2019s where Slydial comes in. The app is free (available for iPhone, BlackBerry and Windows Phone), and it directly dials into a mobile phone's voicemail, so you can simply leave a message.\n\tIn my tests, it worked well most of the time, but on occasion, the recipient's phone rang once briefly before Slydial sent my call to voicemail.\n\tSlydial offers a Premium version, which lets you bypass the ads that sometimes play when you connect to voicemail. But in my tests, I never heard an advertisement.