It is possible to send an SMS message directly from your email without any third-party services. To do so, send an email by entering your recipient's 10-digit cell number followed by the appropriate gateway address for his cell provider. If you are not sure of your recipient's cell carrier, you can look it up with a free service such as FreeCarrierLookup.com, which also provides you with your recipient's gateway address.
For your message to be successfully sent as an SMS, it is recommended to keep your message below 160 characters. If you exceed the 160-character message limit, your message is sent as an MMS message instead. An MMS, or Multi Media Message, may not be supported by some phones and may incur additional charges for your recipient.
There are also several third-party websites, such as Textem.net and SendSMSNow.com, which let you send text messages directly from your Web browser. However, some of these websites require registration, and it isn't always clear how they handle your data and personal information.
Sending an SMS directly from your email client is highly recommended over using third-party services that allow you to send text messages online, since this avoids the risk of compromising your personal information.