I usually bullet proof my buttons like so

<table>
    <tr>
        <td style="background-color: #xxxxxx;">
            <a href="" style="padding: Xpx;">Call to Action</a>

This method is widely supported and provides a maximum tap area on mobile clients. There are, however, a few clients that strip out the padding on the A element displaying it in an almost always broken looking way. Another option would be to pad the TD element instead:

<table>
    <tr>
        <td style="background-color: #xxxxxx; padding: Xpx;">
            <a href="">Call to Action</a>

Although this method has better support, it renders the CTA with a smaller tapable area than the first option.

But what if we refactored by class*ing* the TD and writing a mobile specific media query to unpad the TD and pad the A?
I imagine it would like something like this:

@media only screen and ( -webkit-min-device-pixel-ratio: 0 )
{
    *[class].mobile-btn
    {
        padding: 0 !important;
    }

    *[class].mobile-btn > a
    {
        padding: Xpx;
    }

}

<table>
    <tr>
        <td class="mobile-btn" style="background-color: #xxxxxx; padding: Xpx;">
            <a href="">Call to Action</a>

So before I go off and spend hours testing - do you think it would work?