Until Hindu-Arabic logograms were adopted circa 1000 ce, letters were routinely used by the Phoenicians, Greeks, and others to express numerical concepts. One reason for a conventional alphabetical order was to support this use. 

Using Numbers as sound signs to augment ASCII letters
 

ASCII	New Association	Old Associations	Continuity in shape and reference
1  2 3 4  5 6  7  8  9  10	t, L zh z ng, R (her) dh (the) sh, -- ei, oh th (thin) ei ai (fr9=fry) --	a-alef bird, ox 1-harpoon b- bet house,2  tally marks g-3 tally-marks [=]gG d-delta, daleth, dag-fish f-digamma, wa, fej-viper  e- 6 epsilon, he z- 7-zeta  h- 8 - eta, ch as in loch  th theta - tether iota, yota	The first three numbers are iconic tally marks. They are the same as Roman numerals except for being rotated and cursive. First used by Egyptians.     The two numbers that CCS uses as sound signs are the "look alikes" 2=Zh and 5=Sh. Zh is rare [me5r=measure]. Sh is commonly written as [tio] in TO: [mo'shn = motion = mo'5n].  "5i.p 5 sli'pi 5i'p"[ship 5 sleepy sheep]     The 3 can be viewed as a rotated cursive n and used to mark the /ng/ phoneme found in *bank [ba3g]. This works in handwriting by is visually disruptive in print.The 3 is also related to the ancient yogh symbol which was used by Jones for the vowel in [her].
@  &  ^  (  )  #  <  >	shwa. æ æ u th, dh turned c, th c & k g, aw gamma	at symbol  ampersand  circumflex, carat  bracket  bracket  hash mark, number  less than  greater than	The Eg. open 4 shape was used for "ba" a heron. The closed 4 for was used for hand. The Semites used the 4 for fish (dag) and later renamed it daleth (door). The daleth (delta) with a stem looked like a 4. (see Semitic letter chart)     The Egyptian used the turned h or Y shape for the horned viper looked something like a hook (waw) to the Semites. The viper also looked like an F which the Greeks called digamma. It was used exclusively for the number 5 when the sound was shifted to phi.

Egyptian and Semitic shapes

According to paleographer, Benjamin Sass, the original Semitic letter shapes were borrowed from the Egyptians during the middle Egyptian period (1800-1600 bc). The pictographic and acrophonic notions also played a role in the early alphabet development. 

The objections to using numeric symbols for sound signs

(Critic) "We already confuse 1 and l , 0 and o as well as B and 8. We don't need to add to the confusion by adding a 2 -zh and 5-sh ambiguity. "

(SB) Logically, there can be no confusion since zh and sh are never used without a vowel. 
Examples: 2nd (second) vs. me2r (measure)    5th vs. 5ip (ship)
The F and S are related historically with the long S taking the F shape in 16th century printing. The F in phonecian and greek referred to the number 5.

(Critic) In principle, an orthography should not use digraphs for pure sounds or silent letters as markers.  

When one uses the ASCII character set there are not many options.  This is why Chekt Spelling notation uses numbers (logograms) as sound signs.

The only rationale for keeping the h as a marker is to retain a visual connection to TO. Before 1100, the c was used in this role (scip=ship) where c=ch.  I don't believe that new codes should be non-romic unless there is an over-riding reason. In this case there is. Another option in some typefaces is a small v diacritic above the s and z.

In rapid ryting form the 5 becomes a lazy-h and the 2 a flipped lazy h. As shown on the left, these approximate shapes can be found in Shavian.  In Shavian the symbols refer to tsh and dzh.
 

Can numbers be used as sound signs?

Yes, but they are language specific. "4 Sale" only makes sense in English where four has the same sound as for. In Spanish the sign would be read [kwahtro-sahleh]. 

The four shape [ 4] may be related to the 4th letter in the ancient "alef-bet." It may be related to the daleth (delta).  Until around 800 ad, the letters were used in Greece and the Middle East as numbers so there was a strong association between delta and the concept of four.  Early forms of delta (daleth) had a stem and resembled the 4 shape.

Ancient alphabet design principles

The Semitic orthographers borrowed Egyptian ideas on alphabet design. According to the ancients, the letter shape should resemble a familiar object and the letter sound should be the initial sound in the name of the familiar object. (acrophonic-pictographic) Some of these associations can be used today: B=building, D=door, H=eight

more    phonician letters

Number forms/names vs. letter forms/names

Egyptian number forms and number names were not directly related to letter forms and letter names. Semitic number forms were.  The Semites were into simplification.  The Egyptians seemed content with codes that were more difficult than necessary.  

In one of his short essays, Mark Twain drew a parallel between the Egyptian reluctance to simplify and the resistance that English speakers have against changing their overly complex orthography.

Ancient shapes and significances
 

No. Number	Semitic  Form - see next chart	Semitic Letter Name	Semitic Ref.	Egyptian  Letter  Name	Eg. Letter Reference	English Acro- phonic	Eg. Number Name	Eg. Number Reference
1 2 3 4 5 6 7 8 9 10 20 50 100 1000	k g < G D pfq YY zZ Hh Q i k l m n X	aleph bet, beyth gimel daleth,dag he-epsilon waw-digamma zayin chethheta teth yod, yodh kaaph lamedh mem nun samekh 'ayin pe, pey sadhe qof, kawph resh sin shin taw	ox house camel door hand hook spear barrier . yarn? hand palm rod,cane water snake, fish support . eye mouth ? monkey face tooth tooth mark	alef ..b.. c..  d..  wah.. ts, djed h..  teth	bird leg basket hand chick -i, e -snake twisted-wick thether - - - - -	avian boot cup digits w pad	wa  sen  vethet  wu  tuan  sas  setex  xeshfun  best  met  tuat  -  sa  cha chei	harpoon - - -

Was Egyptian Culture Static

While we think of Egyptian writing and speech as unchanging over their 4000 year history. Pictorial Hieroglyphics were static but shorthand versions (hieratic and demotic)  were developed and these changed over time. The language changed so much that some of the original letter names were lost. In other words, the popular names for the pharoahs hen, flowering reed, and arm changed obscuring the mnemonic. 

Since pictorial hieroglyphics never changed after their introduction around 3200 b.c., we can see the reference but in some cases we have no clue as to the name or pronunciation beyond the sound of the initial letter. 

Sometimes the reference is a little obscure.  Many of the early interpretations have been discredited and one sometimes wonders how solid some of the current interpretations really are.  Some scholars question whether or not hieroglyphics were consistently acrophonic. Perhaps it was the dominant sound which  followed a very weak initial vowel. 
 

Semitic Sound Signs	Egyptian Uniliteral Sound Signs	Greek	TO traditional
	source: hieratic symbos added to a symbol chart found at the URL	Chart alpha yod-iota ayin- omega waw-upsilonbeta-beyt pa-pe-pi f-waw-phi mr-mem-mu nem-nun-nu ro-re-rho h-he-heta	A='alef while the initial sound is a glottal stop the letter is often associated with ah or uh i=any short vowel a=a:

References

Go to Amazon.com and search on number

Danzig, T. Number
Meninger,