Recently, Will Schmitt of Classy posted a blog discussing the limitations of text to give and text to donate services (he distinguishes the two). The blog does point out some interesting considerations, but it overstates the limitations of text to give.
Whether linking a card or a bank account, if the donor only wants to enter credit card/account details once, she will have to create a PayPal or GMG account to store the account details to use in subsequent donations.
When a prospective donor opts in to your keyword, by law you must inform them of the number of future text messages you plan to send them per month. You must also give them clear instructions for how to stop receiving future messages from your organization. We take care of this for you so you don't have to worry about being in compliance.
Every LPFM radio station is required by law to be associated with a charity or nonprofit of some sort. Therefore, SMS donations are a win-win, because they give LPFM radio stations an easy way to fulfill their charitable requirements. Text to give also makes it easier to find sponsors as well as raise funds for their nonprofits.
We have created custom PayPal implementations in the past, but we don't really do it anymore. Basically a programmer has to create a web-based form that has the options, and then pass that data to the PayPal checkout form.