I used to send texts from the server's website when I was with another service. Can I do this with Virgin, I haven't found a way as yet? I have secondary progressive multiple sclerosis and texting is a lot harder than typing on the laptop so it would be soooooo useful.
Try this link: http://microsoft-sms-sender.software.informer.com/1.0/. As it was written for XP you will need to run it in Compatibilty Mode on Windows 7, 8, 8.1, or Windows 10. It can only send 160 character messages though, and you will need to plug your phone in and use it through Bluetooth. It should show up as a Bluetooth modem in the hardware section. If that's no good for you, there are "free" and paid for services by Googling SMS Sender. Please note that the "free" services could be extremely damaging to your computer.
A better alternative in my opinion would be a bluetooth keyboard as they're fairly cheap. You wouldn't need to faff about with your PC. All you would need to do is pair it up with your phone. A lot of them are similar to laptop keyboards.
If you use a Mac the above will not work without major technical know how (dual booting XP on a Mac is or was doable but would be overkill for what you want to do), as the program will only work on Windows. You'll have to use paid services. Free services aren't secure and you don't know who's hosting the sites or where your personal data is going.
You can get Mac style keyboards on ebay as suggested in the above post. Since I am not a Mac user I don't know of any apps (as the like to call them these days) that would do what you want. Most people use PC's on here and Mac stuff is in the minority, but (presumably) if you are using an iPhone and a Mac there should be a way of pairing them up somehow using a Bluetooth dongle.