As is ever the case, and we must have some understanding for our legislators, the law hastens to catch up with technological development, and not always with the celerity that would be desirable (I say this, as I do above, subject to what developments might have occurred meantime in the statutory domain): Textform seems more to be a term defined according to what it is not than by what it actually is. It is "text" contained in a medium that is not otherwise to be defined as Schriftform. That demands agility in finding a neat, unambiguous term to reflect its meaning, first, because written form has since time immemorial been used to translate Schriftform without compunction simply due to the fact there was previously no other way to produce a document than to write it in ink or, later, type or print it. Therefore, till now, one had no cause to ponder whether written form was a proper rendering of Schriftform - perhaps that word should also be a subject of scrutiny. Second, we now have writing that is not per se written but is a file whose content is displayed on a screen (text message) or that is transmitted and put in material form at a distance from its author (e-mail, fax, telex). It is also (as we commonly understand the word) "written" in its form, it is "text", but it is not Schriftform, which applies only to an original, signed document. Third, in an interim stage, the law conceded the admissibility of electronic communications as evidence where an electronic signature was appended, but that clearly rules out the SMS. I wonder even what the status of (the logs of) an online chat message is. So, the challenges are: (i) to review how Schriftform is translated (moving away from written form or in writing would be regrettable, but we have here a breakfast example in which it is actually fairly important to know what's being served - i.e. the two are functional equivalents but are they precise enough in terms of telling contract parties what is a valid communication and what not?); and (ii) to find a term that's broad enough to include what's included in Textform but nothing that isn't and that offers enough breadth to not need revision in the light of new forms of e-communication that might yet come along (on the proviso that those developments would actually be covered by the German term Textform).
Schriftform could perhaps be adjusted to become in an original, signed document. Paper is to be avoided (one recalls the stories of cheques painted on cows as a protest by farmers, which were deemed to be documents; original refers to the judicial best-evidence rules: "original, failing which photocopy, failing which testimony of the writer;" signed is perhaps even superfluous).
Textform could then be in a form of electronic (or electronically transmitted) writing that is not an original document (or is not (legally) an original; or that is not (legally) original). My hesitation here is whether courts (generally) treat e-communications as "originals" under the rules of evidence. If they do, these suggestions will not work and will need refinement.
I toyed with the idea of hard and soft copies, but that introduces parameters into the equation that I'm not able to proceed with (like, is a soft copy still soft if it's printed out? I guess not). While the above (tentative) suggestions may be cumbersome and tend towards glosses, the context in which they would be used, as a contract term, doesn't necessarily demand a swift, elegant solution, rather one that is as accurate as possible.
Naturally, I invite comments and suggestions from anyone with deeper experience of the matter (and who maybe has a simple elegant solution). Whether it's round or square, the hole has some sort of shape: once that's known, we can make a peg for it.