Like MySMS, it would be useful send attachment as a link to a cloud space, instead if sending the attachment as is. Since the most tariff plans doesn't consider MMS but only SMS and Mbyte amount, if you want send cheap an attachment, the only chance is send attachment on a personal cloud space (e.g. DropBox?) or a payed space (e.g. Textra extra payed account?), give back a short URL to the uploaded file, and write this URL in the SMS.
I report that non all of my contacts has a correct setup in their phones, and they can't anyway receive MMS correcly sent by me: receiving a simple SMS with URL to the attachment, they can access the file whatever SMS client they use.