We actually used to have a short code, but recent changes from the cell phone providers (ATT/Verizon/etc) have caused all donation platforms, including ours, to have to remove that option for our customers.
We aren't thrilled about it either, but as long as you are asking your donors to save the number in their contacts, they should only have to enter that number once.
To our knowledge, the only way to get a shortcode is by going through Mobile Giving Foundation. Last we heard, it can take anywhere from 8-12 weeks to get everything set up and the cost is quite high at around $1,000 per month just to lease a short code, and they require a minimum 6-month contract. That's only even if you qualify in the first place. It's usually pretty cost-prohibitive to most organizations.
All of that said, we are always looking for ways to improve the donor experience. If a new and easier way for donors to text in becomes available, we will certainly be looking into it.
A simple alternative might be utilizing the QR Code that is included with your account. When your account's QR Code is scanned, it will automatically open a texting app on the donor's phone, enter your account's giving number, and insert GIVE as the keyword. All the donor will have to do is scan the QR Code and hit send!