Yeah, I have, and it sucks. Most of the time. And it's expensive. And I won't change my opinion that you can achieve the same grade of simplicity and ease of use and functionality through completely FREE email.
Email requires data no? Therefore the receiver needs to have a data plan or it becomes expensive for them and they have to have an email account setup on their phone.
Also many tariffs in the UK at least take MMS as part of the free allocation of SMS albeit at a rate of 4 to 1. All phones these days (expect the iPhone) come with native MMS so the user will simply receive the picture message for free.