I've been looking at sending text messages from an Arduino type development board, with the ability to text back to the processor from a mobile phone. The cheaper modules which work on 2G are effectively obsolete in the UK, and the 4G modules are quite expensive. Since a number of processor boards now have built-in WiFi is there a cost effective way to send and receive messages over the web? Something like WhatsApp but without the processor board having a phone number....

 

I've been looking at sending text messages from an Arduino type development board, with the ability to text back to the processor from a mobile phone. The cheaper modules which work on 2G are effectively obsolete in the UK, and the 4G modules are quite expensive. Since a number of processor boards now have built-in WiFi is there a cost effective way to send and receive messages over the web? Something like WhatsApp but without the processor board having a phone number....

Check out Twilio. They have an amazingly complete portfolio of communications services, and excellent API, and won't break the back (pre-paid, usage sensitive). The API would allow direct sending from your board. For receiving, you would need to work out a dispatcher that received the messages and forwarded them to the board via whatever protocol you'd like.

The dispatcher bit could be a something like an NGINX front-end and a trivial script on the back end. You would need a publicly available compute node of some kind but the very cheapest offerings from Amazon AWS (potentially free!), Microsoft Azure, Akamai Linode (not free but can be dirt cheap), Digital Ocean (also very cheap) , &c. would serve more than admirably and could have utility for other things. I have personally used all of these services but I have used Linode for more than 15 years now and can certainly commend them to you.

The only other suggestion I have is Telegram. It can be used for messaging though you will have other have the Telegram app on the device sending the messages—on the other side you will use Telegram's API. The device you are communicating with will be a "bot" on Telegram. I haven't tried to use it with an MCU, but there is no reason I can see that it couldn't work.

 

Actually, I do have one more suggestion. An alternative to Twilio that reduces regulatory burden (you are going to find that SMS has become a tangle because of efforts to stop spam) is VoIP.ms. They are a Canada-based VoIP provider and just recently their API has exposed the ability to receive and send SMS using a phone number you've added to your account.

The US numbers are about a buck a month to maintain and they have usage sensitive and flat rate options. The UK numbers would cost me about $4.00USD/mo. The one complication is that I can't tell if they support SMS or not.

I am in the process of moving things that are currently using Twilio for SMS over to VoIP.ms to simplify my life, but Twilio is a wonderful offering.

 

Check out Twilio. They have an amazingly complete portfolio of communications services, and excellent API, and won't break the back (pre-paid, usage sensitive). The API would allow direct sending from your board. For receiving, you would need to work out a dispatcher that received the messages and forwarded them to the board via whatever protocol you'd like.

The dispatcher bit could be a something like an NGINX front-end and a trivial script on the back end. You would need a publicly available compute node of some kind but the very cheapest offerings from Amazon AWS (potentially free!), Microsoft Azure, Akamai Linode (not free but can be dirt cheap), Digital Ocean (also very cheap) , &c. would serve more than admirably and could have utility for other things. I have personally used all of these services but I have used Linode for more than 15 years now and can certainly commend them to you.

The only other suggestion I have is Telegram. It can be used for messaging though you will have other have the Telegram app on the device sending the messages—on the other side you will use Telegram's API. The device you are communicating with will be a "bot" on Telegram. I haven't tried to use it with an MCU, but there is no reason I can see that it couldn't work.

Wow, many thanks indeed for this complete reply, I'll spend some time exploring these options