Juan,
The mobile wallets can only send with InstantX. If you want a store to detect the InstantX, that is still getting worked on. The Dash N Drink source that can detect an InstantX is still getting a few final bugs worked out and once that is complete it is possible to use that system for Instantx receiving with a small computer Raspberry PI or any desktop. The merchant can also use a desktop wallet and verify the instantX by looking at the incoming transaction. This isn't an easy solution yet....I want this to get better.
I would also expect mobile wallets to get instantX receive working soon, but I don't have a definite time frame. All the wallets can receive the funds, they just won't tell you if it was an instantx or not.
Like thedashguy said, these are the two most stable wallets. (With the android version you may need to go into settings toggle off and on instantx for it to show up when sending a payment. The apple wallet requires a computer to install, they are working on getting it in the app store soon)
android: play store or
https://play.google.com/store/apps/details?id=hashengineering.darkcoin.wallet&hl=en
iOS:
https://dashtalk.org/threads/iphone-dashwallet-release.7123/
The fulltimegeek android wallet is a redesign with simpler interface. I still don't think it is ready for primetime, but it is close and more features are added frequently.
https://github.com/fulltimegeek/Dash-Wallet