can a point mutation cause a frameshift?
I saw the OP edited it's question quite a lot.. This answer answers the questions before the edit, I will not delete this because it will maybe help other people
I'm not sure if you fully understand the terms you used so I will start with clarifying these.
Missense mutation


  a point mutation in which a single nucleotide change results in a
  codon that codes for a different amino acid (wiki)


Example

    DNA: 5' - AAC AGC CTG CGT ACG GCT CTC - 3'
         3' - TTG TCG GAC GCA TGC CGA GAG - 5'
   mRNA: 5' - AAC AGC CUG CGU ACG GCU CUC - 3'
Protein:      Asn Ser Leu Arg Thr Ala Leu

-------------------------↓↓↓↓↓↓↓--------------------------
    DNA: 5' - AAC AGC CTG CTT ACG GCT CTC - 3'
         3' - TTG TCG GAC GAA TGC CGA GAG - 5'
   mRNA: 5' - AAC AGC CUG CUU ACG GCU CUC - 3'
Protein:      Asn Ser Leu Leu Thr Ala Leu


The 4th codon which was CGT (and GCA on the other strand) is changed because of a subtitution of the G for a T. Because of this change the codon will not code for Arg anymore but instead it will code for Leu. So a missense mutation causes the sequence to be in the same frame as before however a codon is changed and subsequently an other amino acid is added to the polypeptide chain during translation (this is not always the case see wobble)


Frameshift mutation


  A frameshift mutation (also called a framing error or a reading frame
  shift) is a genetic mutation caused by indels (insertions or
  deletions) of a number of nucleotides in a DNA sequence that is not
  divisible by three. (wiki)
  Example


    DNA: 5' - AAC AGC CTG CGT ACG GCT CTC - 3'
         3' - TTG TCG GAC GCA TGC CGA GAG - 5'
   mRNA: 5' - AAC AGC CUG CGU ACG GCU CUC - 3'
Protein:      Asn Ser Leu Arg Thr Ala Leu

-------------------------↓↓↓↓↓↓↓--------------------------
    DNA: 5' - AAC AGC CTG CTT ACG CT C    TC - 3'
         3' - TTG TCG GAC GAA TGC GA G    AG - 5'
   mRNA: 5' - AAC AGC CUG CUU ACG CU C    UC - 3'
Protein:      Asn Ser Leu Leu Thr Leu ..........


In this case the nucleotide T is removed and thus causing a framehift because we need tree bases to form a codon. by removing a nucleotide we just read further till we find a third base and this will be our "new" codon. This new codon does not code for Ala anymore but will code for Leu. (I added the dots because of the fact that the stop codon will/can be shifted and the transcript can be either shorter or longer (the previous stop codon will no longer exist). 




  Could a missense mutation cause a frameshift


In the case of a missense mutation the DNA sequence will be in the same frame (no nucleotide is added or removed) and in the case of a frameshift a nucleotide needs to be added or removed and therefore a missense can't cause a frameshift.


  such that a mutation results in the sequence AUG?


Both a missense and a frameshift could result in a start codon.
Example (frameshift)

mRNA 5'     AAC AUU GAC 3'
Protein:    Asp Ile Asp
    -------------------------↓↓↓↓↓↓↓--------------------------
mRNA 5'     AAC AU G  AC.... 3'
Protein:    Asp Met   ........


Example (missense)

mRNA 5'     AAC AUU GAC 3'
Protein:    Asp Ile Asp
    -------------------------↓↓↓↓↓↓↓--------------------------
mRNA 5'     AAC AUG  GAC 3'
Protein:    Asp Met  Asp


So both a frameshift mutation and a missense mutation can introduce a Met --> a start codon.


  a mutation results in the sequence AUG to be present in the transcript
  but upstream the start codon?


A gene is only transcribed if this gene is preceeded by the appropriate sequences: 

The start codon will be present in the first exon so the only way to put a start codon before the "old" start codon while remaining all other sequences(UTR,promtor, enhancers etc.) in tact is to "create" one just behind the 5' UTR and before the "old"  start codon in the first exon. This can be done by just inserting AUG in there, HOWEVER we are talking about point mutations:


  A point mutation, or single base modification, is a type of mutation
  that causes a single nucleotide base substitution, insertion, or
  deletion of the genetic material, DNA or RNA
  


The start codon we are talking about is positioned AFTER the 5' UTR (as said above):



By inspecting the "general" 5'UTR sequence we can see that there are already "start codons" (not really start codons because they are not translated") present before the start codon. We could probably add one using a frameshift or a missense mutation as described above and in your edited question:


  If the new ATG is close enough to the original one (so that it is
  within the processed transcript and downstream of a ribosome-binding
  site) and in frame, it will be used to initiate translation, adding
  amino acids to the amino terminus of the original protein


As far as I can reason is the only way to create a start codon BEFORE the old one is to change the UTR. As stated in your queation this can only "work" if the UTR parts which have an important function are not affected. Further to get this working the 5'UTR should contain a (not "important" )sequence which can be mutated tot form an AUG (see my explanation above)